Posted by Site Moderator Webmaster on Sunday, July 25, 2021,
In :
Mineralogy
by
Duncan Miller
Inspired by
an article by Pavel Martynov on mindat.org I have been experimenting with
taking stereoscopic pair photographs of an otherwise rather uninteresting
mineral specimen, so that it can be viewed in 3D. It is really simple. All you
need do is rotate the specimen through five degrees, without otherwise changing
its relationship to the camera, and taking two photographs of it. Then you swap
the righthand photo for the left one, and view the pair by squinting. You can
p...
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JOURNEYS IN PEGMATITE PARADISE
Posted by Site Moderator Webmaster on Sunday, July 25, 2021,
In :
Mineralogy
by
Duncan Miller
South
Africa is famous for its gems and minerals, and visitors sometimes imagine they
can pick diamonds off the soles of their shoes. Gold nuggets roll down streams
and platinum can be picked out of some of the oldest rocks on Earth. This is
all fantasy of course. The platinum, gold and diamond mines are so regulated
that throughout their lives most South Africans never see native gold, or
platinum, or an uncut diamond; and possessing them without a permit is a
criminal offe...
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BOOM AND BUST - THE COPPER MINING TOWNS OF NAMAQUALAND
Posted by Site Moderator Webmaster on Wednesday, June 23, 2021,
Duncan
Miller
"Their dress consists of all kinds of beautifully prepared
skins...gorgeously ornamented with copper beads...Their locks they thread with
copper beads, covering their heads all over.
Around their necks they have chains, slung round them 15 or 16
times. Many have round copper plates
suspended from these chains. On their
arms they have chains of copper and iron beads which go round their bodies 30
or 40 times. Their legs are encased in
plaited skins, ornamented with beads......
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COLOUR-CHANGE GARNETS – THE USAMBARA EFFECT
Posted by Site Moderator Webmaster on Monday, May 24, 2021,
In :
Mineralogy
Duncan Miller
There are several different mechanisms for
garnets to show a change of colour. The most common of these is analogous to
the colour change in the well-known alexandrite variety of chrysoberyl. This is
due to differential transmission of different wavelengths of visible light,
leading to a difference in perceived colour under lighting with different
degrees of red or blue light. A less well-known type of colour change in
gemstones is the so-called Usambara effect, named after t...
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COLOUR, ZONING AND FALSE COLOUR IMAGING IN GARNETS
Posted by Site Moderator Webmaster on Monday, May 24, 2021,
In :
Mineralogy
Lesley Andrews
Garnets are not only attractive, but also useful. As
residents of the Cape, many of us know about the use of garnets as markers in
diamond exploration. Other examples include garnet use in sandpaper, especially
for wood sanding, and the production of synthetic garnets for laser generation.
The colours of garnet group minerals and varieties is
a complex subject. Not all garnets are red, in fact they are found in all
colours except bright blue. Briefly, the most common ions inf...
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THE GARNET GROUP
Posted by Site Moderator Webmaster on Monday, May 24, 2021,
In :
Mineralogy
by
Peter
Rosewarne
This month we are checking out the garnet group of minerals, which
most people will have come across in the form of jewellery, as mineral
specimens and even in mundane articles such as sandpaper. The previous fluorite
article started with some “C” words that apply to the mineral and in the same
vein, the following apply to garnets, with some
qualifiers; cubic, contain calcium (some), colourful (some), cleavage-free,
conchoidal fracture, costly (some), contain chrome ...
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Hidden Treasures
Posted by Site Moderator Webmaster on Tuesday, April 27, 2021,
In :
Mineralogy
Jo
Wicht
Who would have thought that some of the most boring looking
mineral specimens could be the most spectacular under shortwave fluorescent
light? Look at these three, for example…
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DISTINGUISHING RUBY FROM GARNET AND RED GLASS USING FLUORESCENCE
Posted by Site Moderator Webmaster on Monday, April 26, 2021,
In :
Mineralogy
Duncan Miller
Cut rubies,
red garnets and red glass can look very similar. There are several techniques
that can be used to determine if a red stone is a ruby. These include a
semi-destructive relative hardness test (ruby will scratch garnet and glass,
but not the other way around); using a polariscope to test for birefringence
(ruby is birefringent whereas glass and most garnet are not); and using a dichroscope
to see the two pleochroic shades of red in ruby (which are absent in garnet and
...
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Feldspar, or so I thought….
Posted by Site Moderator Webmaster on Monday, April 26, 2021,
In :
Mineralogy
Willie
Lombard
I
collect different species of minerals and rocks of SA and Namibia and need only
one good example of each. Right across from the old Swanson Enterprises
building in Springbok is an open yard with some large heaps of rocks and
minerals. I asked the resident on the property if I could have a look-around.
No problem. Found some fluorites and a good example of a diorite. There were
some feldspars and a lot of pegmatites. I was sleeping over, so I asked the
resident if I could ret...
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Yooperlites of Pilanesberg
Posted by Site Moderator Webmaster on Monday, April 26, 2021,
In :
Mineralogy
Willie
Lombard
On
the shores of Lake Superior in the USA a fluorescent rock made headlines (on
YouTube, anyway!). They call the normally drab rock a Yooper, after the
locals from Upper Michigan. A geologist from the local university found that
the sodalite in the rock causes the yellow fluorescence. I wish my sodalite
would fluoresce like that! Those that do, produce only a very weak yellowish glow.
On
my way to the Groot Marico Gemboree in 2018 I decided to sleep over in the
Pi... |
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FLUORESCENCE IN MINERALS: A BRIEF INTRODUCTION TO WONDERLAND
Posted by Site Moderator Webmaster on Monday, April 26, 2021,
In :
Mineralogy
By
Peter Rosewarne
Introduction
The
branch of mineralogy dealing with fluorescence apparently gained
popularity in the 1930s with the availability of battery-powered portable
ultraviolet (UV) lamps. The pioneer in producing such UV lamps and using them
to prospect for and showcase minerals was Thomas S Warren, after whom the
Thomas S Warren Museum of Fluorescence at Sterling Hill Mine Museum in the USA
is named.
Those
of you who have been paying attention to previous MinChat articles will
...
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TRIALS AND TRIBULATIONS WITH CUT GEMSTONE HEATING
Posted by Site Moderator Webmaster on Thursday, March 25, 2021,
In :
Lapidary
Duncan Miller
Inspired
by the dramatic change in colour of the large tourmaline illustrated in last
month’s Mineralogical Chatter, that went from autumn brown to a purplish-pink
on heating by the client for whom I had cut it, I decided to experiment myself.
A friend lent me a small ‘enamelling’ kiln; I bought a suitable crucible from
jewellers’ supplier Lipman & Son in Cape Town (https://lipmanson.co.za/);
and Ian Lipman generously gave me jewellery casting investment powder to
protect...
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Six of the Best Specimens in the Mineral Kingdom!
Posted by Site Moderator Webmaster on Thursday, March 25, 2021,
In :
Mineralogy
By
Peter Rosewarne
Introduction
Have
you ever wondered if there was a specimen out there that was the world’s best,
or what the best six or ten mineral specimens ever discovered are considered to
be? I thought it might be a bit of fun to put together a “Six of the Best” of
the mineral kingdom based on expert opinion in respected publications, such as
The Mineral Record and its supplements, Masterpieces of the Mineral Kingdom,
and American Mineral Treasures. Some of these discoveries g...
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THE MOST DIFFICULT JIGSAW PUZZLE OF ALL TIME
Posted by Site Moderator Webmaster on Wednesday, February 24, 2021,
by
Duncan Miller
Imagine
a jigsaw puzzle the size of the Earth, with most of the pieces missing. And
those that aren’t missing are moving around all the time. This is the task that
confronts some ambitious geologists. It is important because it explains why
there are oceans and mountain chains, and why we may find rocks of similar ages
and composition on far-flung continents. It also satisfies human scientific
curiosity, and keeps some people employed and off the streets.
Until
the mid-1960s...
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Botryoidal Minerals: A Colourful Trip Around the Mineral Kingdom
Posted by Site Moderator Webmaster on Wednesday, February 24, 2021,
In :
Mineralogy
by
Peter Rosewarne
Introduction
My
previous MinChat article on fluorite described a colourful trip around the
world. In this article we take a colourful trip around the mineral kingdom,
using minerals with a botryoidal habit as the guide. The idea came from the
supplement to The Mineral Record of January-February 2020 on Mineral Collectors
in Arizona, with the focus of one of the collectors being on botryoidal mineral
specimens. The term botryoidal is
derived from the Greek word botryios
or ...
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FLUORITE - A COLOURFUL JOURNEY AROUND THE WORLD
Posted by Site Moderator Webmaster on Friday, January 15, 2021,
In :
Mineralogy
by Peter Rosewarne
Fluorite: cubic, common, cheap (comparatively, but
can be costly), contains calcium, and colourful, are some of the "C"
words that can be used to describe this mineral. While good specimens of fluorite from classic
localities aren’t cheap, most are cheaper than good specimens of ‘higher-end’
minerals such as azurite, dioptase, tourmaline and beryl and it is possible to build up a good collection of
fluorites from worldwide localities. You are also likely to get a nice-...
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SAMS outing to the Springbok area, September 2020
Posted by Site Moderator Webmaster on Friday, December 4, 2020,
Lesley Andrews
Jubilee
copper slag dump, near Concordia
Towards the end of September, Richard and I met up
with some members of SAMS (South African Micromount Society) in the Northern
Cape. The Society is based in Gauteng, and the trip included site visits en
route from Johannesburg. The Chairman of SAMS, Patrick Barrier, and Linda
Stone, the President of FOSAGAMS, also joined the outing.
In the Northern Cape we stayed in accommodation at
Springbok and Nababeep. This area is well-known for cop...
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Springbok Recce: Geology, Mining Heritage (and Wild Flowers)
Posted by Site Moderator Webmaster on Friday, December 4, 2020,
By Peter Rosewarne
Figure
1 The Matzikammaberg at Vanrhynsdorp
This
trip had its beginnings during the Lockdown with reading up on some books on
South Africa’s mining heritage, geological sites and geological journeys. With
the relaxation of travelling restrictions and reports of a bumper flower season
in Namaqualand, I decided on the spur of the moment to do a trip to the
Springbok area, which is rich in sites of geological and mining interest. My
wife and I were going to go but, in the we...
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SOME UNUSUAL POLISHED SLABS
Posted by Site Moderator Webmaster on Monday, October 26, 2020,
Peter Rosewarne
Polished
slabs and spheres don’t usually figure highly in my wish-list of mineral
specimens but, over the years, some colourful and interesting ones have caught
my eye and have been added to the Rosey Collection. This short article
highlights some of what I hope you will agree are both unusual, interesting and
colourful polished slabs from various localities around the world. The slabs
very briefly described and illustrated herein are Sonora Sunrise and Laguna
Agate from Me...
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PICKY PIGEONS PREFER POLISHED PEBBLES
Posted by Site Moderator Webmaster on Monday, October 26, 2020,
Lesley Andrews
I am the proud owner of two stone plants which I keep
on the stoep table - these are decorated by a surface layer of small
tumbled semi-precious stones. Recently I was astonished to see a threesome of
Cape Turtle Doves on the table carefully picking out some of the stones,
passing them to each other, rolling them around in their beaks and putting them
down carefully all over the table. I knew that many birds eat grit, but why
this preference for my ornamentals?The
Cape Turtle Do... Continue reading ...
DIGGING OUT DUMORTIERITE
Posted by Site Moderator Webmaster on Saturday, September 26, 2020,
In :
Mineralogy
I do give myself complications.
Based on the success of the “September Spheres”,
we invited photos of “royal blue” minerals for our October newsletter. This is
because we are featuring Peter’s detailed article on lapis lazuli. Ultramarine
is such a rich colour and there are not that many minerals of such a classic
blue.
For my contribution, I photographed the
few possibilities I had in my mineral cabinet, but thought a bit more. There
was an odd offcut of stone in the outside cupb...
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LAZURITE – A TUCSON STORY
I first visited the Tucson shows in 1992. My intention was to buy
faceting rough, but there was almost none I could afford, although the
rand/dollar exchange rate was 6:1. One day, walking around with my friend and
research colleague David Killick from the University of Arizona we wandered
around, dazed and bewildered by the spectacular minerals from Afghanistan on
display in one of the numerous tented venues. On one table, crowded with Afghan
ethnic jewellery, possibly all modern, there sat ...
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LAPIS LAZULI: EAST VS WEST
Posted by Site Moderator Webmaster on Friday, September 25, 2020,
In :
Mineralogy
Peter Rosewarne
And
now for something completely different, from me at least. I don’t normally
write about semi-precious ornamental stones/rocks but felt there was a story in
this one based on a long-ago overseas trip, a more recent article in the
Mineralogical Record, some carvings I have from the former and some mineral
specimens related to the latter.
Firstly,
some technical clarity about lapis lazuli, or ‘lapis’, which many of you
probably don’t need. I had always thought that ...
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PLAYING WITH QUARTZ SPHERES IN POLARISED LIGHT
Posted by Site Moderator Webmaster on Monday, August 24, 2020,
In :
Lapidary
Duncan Miller
It’s play time! For this exercise you need a flat computer screen with an
open blank Word page, a smallish clear quartz crystal, a quartz sphere if you
have one, or if not, some clear quartz beads (glass beads won't work), plus a
pair of cinema 3D glasses or Polaroid sunglasses.
Quartz
crystals are anisotropic. This means that a ray of light travelling through the
crystal is split into two polarised rays, vibrating at right angles to each
other. There is only one directio...
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Stories Behind Some Recently Acquired ‘Exotic’ Rocks and Polished Spheres
Posted by Site Moderator Webmaster on Sunday, August 23, 2020,
In :
Mineralogy
by Peter Rosewarne
With
the lockdown in force it’s given me some time to revisit my passion for igneous
rocks and their minerals, being what we used to call a ‘min and pet’ man whilst
studying geology at Kingston University back in the early 70s. Of particular
interest to me on the local scene are the Bushveld Igneous Complex, the
Pilanesburg Alkaline Complex, kimberlites, ultramafics and the Vredefort
Dome. In my quest to find specimens of
the ‘type’ rocks from these sites, in a...
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RECYCLE, REUSE, REPURPOSE – THE CAPE TOWN TIN MINES
Posted by Site Moderator Webmaster on Monday, July 27, 2020,
In :
Mineralogy
Duncan Miller
This month we are going to do all
three, recycle an old publication, reuse it with additional photographs, and
repurpose it as an article on the club’s website. The article describes Cape
Town’s former tin mines, and the website article has a virtual tour of the
Vredehoek tin mine on Devil’s Peak, courtesy of Dr Gregor Borg of Halle
University in Germany. All of this is
available for download from http://ctminsoc.org.za/resources/CAPETOWNSTINMINES.pdf
Few people know that ...
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MINERAL OF THE MONTH – OLIVINE
Duncan Miller
Olivine
is the name given to both a mineral and a mineral group. The mineral olivine is
an orthorhombic silicate with the relatively simple chemical formula of (Mg,Fe)2[SiO4].
It has a continuous range of composition between two end members, one
magnesium-rich and the other iron-rich. The magnesium end member of the range
is called forsterite (Mg2SiO4) and the iron end member is
fayalite (Fe2SiO4). These distinct minerals form part of
the olivine group, which also includes a mang...
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FABERGE’S BIRDS
Posted by Site Moderator Webmaster on Monday, July 27, 2020,
In :
Lapidary
Lesley Andrews
Peter Carl Fabergé was born in St Petersburg in 1846, and
eventually became Goldsmith to the Imperial Court of Russia, and a supplier of
wonderful artworks worldwide. He assumed charge of the workshop his father had
established in St Petersburg when he was only twenty-four years old, and
presented the first Imperial Easter Egg to the Russian royal family in 1884.
The workshop survived until 1918, by which time Russia had succumbed to
revolution and the royal family was no mor...
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A GEM CUTTER’S JUNK BOX
Posted by Site Moderator Webmaster on Thursday, June 25, 2020,
In :
Faceting
Duncan Miller
After
several years, or after many years, a gem cutter lands up with a junk box. Mine
contains disappointing stones abandoned in disgust and partly-worked stones
that came over the years with various faceting machines and batches of rough.
As a lock-down project I decided to see what I could make from the contents of
the faceting junk box. (There are another two – one with cabochons and another
with broken synthetics. You never know, you know…)
To
make it something of a ...
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A MINERAL COLLECTOR’S SHOW BOX
Malcolm Jackson
The
Blue Lace Agate article by Jo and Duncan in last month’s Mineral Chatter
inspired me to make a box and as I had some really nice pieces of Yellowwood
around, I got sawing and made the box you see in the picture. I made the box
300 mm × 400 mm × 100 mm deep. I hope to catalogue the specimens and add some
artwork. I also want to include Jo and Duncan’s article in a booklet format.
I wanted to house
some of my Blue Lace Agate specimens that I had collected over many... Continue reading ...
TIME
Posted by Site Moderator Webmaster on Thursday, June 25, 2020,
In :
Mineralogy
Duncan Miller
Our individual lives are so short, and geological time so long,
that it is difficult to comprehend ‘deep time’, the most awe inspiring aspect
of geology. Geologists often seem to work in units of a million years, as
though that is the basic unit for the passage of time on Earth. So let’s make
some effort to comprehend geological time – after all it is what makes geology
tick.
Consider a rare, long-lived human life span of 100 years. There
would be 10 000 of those in a ...
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The World of Tourmaline (in brief)
Posted by Site Moderator Webmaster on Thursday, June 25, 2020,
In :
Mineralogy
Peter Rosewarne
I’ve borrowed the title of a new coffee table book by Gerhard
Wagner for this article as it seems appropriate in that the Tourmaline Group
encompasses some 14 species currently and it is found in classic localities
around the world. The idea for doing this article came from a comment from Jo
that EXCO had raised tourmaline as a possible discussion topic. I also have and
have had quite a few tourmaline specimens in my collection over the years and
have attempted to limit dis...
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COVID-19 eclipses the Amazonite clouds
Posted by Site Moderator Webmaster on Sunday, May 24, 2020,
In :
Lapidary
by
Jay and JD Haasbroek
I know for
sure it was last year some time, but that’s about all I am prepared to admit to
any sense of time or space in these times.
As was
usual back then Verna Jooste was visiting round the kitchen table with me, and
Jay was busy with stones in her adjacent cutting studio and joining the
conversation every so often, with a stone in her hand. Verna, a teaching
jeweller and artist, is always interested in the stone in the hand. She comes
from a family of diamond c...
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BLUE LACE AGATE FROM YSTERPUTS, SOUTHERN NAMIBIA
Posted by Site Moderator Webmaster on Sunday, May 24, 2020,
In :
Mineralogy
by Jo Wicht and Duncan Miller
For
several decades small mines in southern Namibia have produced an attractive banded
agate marketed as lapidary material. The major source has been a mine on
Ysterputs farm, producing blue lace agate. It was promoted widely by the late
George Swanson who owned the mine, so this material with its wavy blue and
white lines is quite familiar. What is less well known is that the blue lace
agate from Ysterputs is accompanied by several minerals forming aesthetic,
c...
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HOW TO KEEP YOURSELF BUSY WHEN UNDER HOUSE ARREST
Posted by Site Moderator Webmaster on Saturday, April 25, 2020,
Duncan
Miller
When
you have finished the chores, tidied the garage, weeded the garden, washed the
windows, painted the house and knitted the dog a winter coat, how do you
keep yourself busy around the home during lock-down? You could take advantage
of the enforced holiday to photograph and catalogue your mineral collection,
even if you are not preparing it for sale.
Bonnie,
decked out in MinSoc green (courtesy of Jo Wicht)
Photography
of minerals need not involve very expensive equipment. My...
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GROTTOS, ANCIENT AND MODERN
Posted by Site Moderator Webmaster on Saturday, April 25, 2020,
Lesley
Andrews
A grotto is
“a natural or artificial cave used by humans in both modern times and
antiquity” (Wikipedia). Grottos are fascinating subjects for a mineralogist –
the article below deals with European grottoes, but there are also grottos of a
different kind in north Africa and China.
Natural
grottos are often found near water and may flood at high tide, such as the
famous grottos around the Mediterranean and Adriatic Seas, often accessible by
swimming or diving. Inland, grot...
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SOME REFLECTIONS ON STARTING A MINERAL SPECIMEN SALE WEBSITE
Posted by Site Moderator Webmaster on Tuesday, March 24, 2020,
In :
Mineralogy
by
Peter Rosewarne
About a year
ago I wrote an article on selling a mineral collection from South Africa, which
was featured in the MinChat. One of the methods I listed, unsurprisingly, was
setting up my own internet site. I didn’t go that route initially, relying on
selling back specimens to dealers such as Hummingbird Minerals, John Betts Fine
Minerals, Fabre Minerals and The Mineral Gallery, and some on Club Open Days.
However, the former route seems to have run its course in terms of ...
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Richtersveld Revisited
Dave Hawes
I
was lucky to be able to go on the trip that the club recently organised to the
Richtersveld but unfortunately unable to attend the report back a few months
later.
As
I have been able to visit the area on numerous occasions, for a variety of
reasons, since my first visit in the early 1980s I thought that I could share
some of my experiences with the club.
While
I had visited Namaqualand as a typical tourist to see the flowers, my first
serious visit in the early 1980s was to del...
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A Gneiss Change: New trends in Scottish Lapidary
Posted by Site Moderator Webmaster on Saturday, January 18, 2020,
by Lesley AndrewsOn a recent
visit overseas, Richard and I travelled around the Scottish coast, including
the Highlands and Islands. I found that nothing had changed weather-wise in the
country of my birth – rain in the west, and wind in the east – but that new
varieties of ornaments and jewellery are now available country-wide. The
factors driving these changes are the increased number of potential buyers
(tourist numbers have rocketed; on top of this there are now many on-line
orders), ...
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FACETIPS - AN ‘EPIDOTE’ ANECDOTE
Posted by Site Moderator Webmaster on Sunday, November 24, 2019,
In :
Faceting
Duncan Miller
A few years
ago, faceting friends of mine in Durban bought some green gem quality material
sold as epidote or possibly peridot. It was nice clear green, and some pieces
of rough still adhered to a matrix, "dug out of the ground right in
front" of the vendor from Moçambique. The cutting and polishing was easy,
apparently working like tanzanite. But the surface of the polished stone
degraded quite rapidly, developing hazy spots, so samples were sent to me for
identification.
The ...
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FACETIP – POLISHING REALLY TROUBLESOME FACETS
Posted by Site Moderator Webmaster on Friday, October 25, 2019,
In :
Faceting
Duncan Miller
Polishing
soft gem materials, Mohs’s hardness 5 and less, and facets near the cleavage of
some harder materials can be very difficult with commonly used polishing laps.
Some years ago, Gearloose Lapidary (www.gearloose.co) introduced
the Lightside™ lap, intended specifically for polishing soft materials. It is a
‘reduced-friction’ composite lap, used with diamond or oxide slurry to produce
flat facets without significant edge rounding. It is described as a ‘durable,
p...
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KYAWTHUITE, THE RAREST MINERAL, FOR NOW…
Posted by Site Moderator Webmaster on Wednesday, September 25, 2019,
In :
Mineralogy
Duncan Miller
Reproduced by courtesy
of the Natural History Museum of Los Angeles County
Every year,
the International Mineralogical Association approves the names of many newly
discovered minerals (http://nrmima.nrm.se//recentmin.htm). The
requirements are stringent, involving analytical descriptions of both the
chemistry and physical structure of any candidate new mineral. Most of these
are microscropic and not display-worthy. But every now and then, a new mineral
is discovered that not only ...
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Madagascar - the Road to Hell-Ville
Mandy
Freeman
With a sense
of excitement and anticipation of the mineral treasures Madagascar offers, we
boarded Air Madagascar on 1st July this year (okay, 4 hours late,
but at least on the same day). Our trip was part rock-hunting (obligatory in
the Freeman household), and part island-holiday. Boy, were we in for a
surprise…
We arrived in Antananarivo, capital of Madagascar where our
adventures in a hired 4x4 with driver began. Tana, as it is known, has several
stone markets where you...
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My New Toy
Posted by Site Moderator Webmaster on Sunday, August 25, 2019,
In :
Faceting
by Duncan Miller
A few months
ago I bought an Imahashi faceting machine, Faceting Unit Model FAC-8C, the
earlier of two models. This one dates from 1970, co-incident with when I
started faceting. Sometime during the 1970s my father owned one briefly, but I
took no notice of it then. Now it intrigued me, because it is a platform
machine, unlike the more familiar mast machines. Platform machines have several
attractive features. You can lift the entire handpiece free of the machine to
inspect th...
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Return to Tubussis reveals Surprise
Posted by Site Moderator Webmaster on Sunday, August 25, 2019,
by
Mandy Freeman
During one of
the excursions arranged at the 2019 Gemboree, a group of enthusiasts decided to
split from the main convoy to return to Tubussis to spend a little more time
looking at what this tiny village has to offer. The Green Dragon Mine is
located near to Tubussis, and the area is known for good quality demantoid or
green garnets. One of the vendors had laid out tables, which due to time
constraints, the convoy missed on the first visit, and some very nice
aquamarine spe...
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Rocking the Richtersveld 2019
Posted by Site Moderator Webmaster on Sunday, August 25, 2019,
‘Oh, oh, oh,
matchbox full of diamonds
pocket full of rain
I'm as happy as a hotel in the springtime
when the flowers bloom again’
David Kramer’s song about the
Richtersveld starts on the road to Lekkersing: “O ja, vanaand stap ek alleen op
die pad na lekka sing.”
It came bubbling into my brain the
night we were briefed that we would be on the road to Lekkersing the next
morning, deep in the Richtersveld, deep in diamond country, and it all seemed
to make a new kind of sense. We w...
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FACETIPS
Posted by Site Moderator Webmaster on Wednesday, July 24, 2019,
In :
Faceting
By Duncan Miller
How to teach yourself faceting, in three easy steps:
1.
Acquire a faceting machine. https://facetorsguild.com.au/About-Faceting-Machines
2.
Learn to facet. https://www.gemsociety.org/article/lapidary-fundamentals-gemstone-faceting/
3.
Become an expert. https://www.youtube.com/watch?v=oD6ZlNmtwmM&list=PLFIMjYf_BtnvaVZNQkHJ4ieF-v1fqPgqu&index=2
These are good
introductory lessons for those starting out faceting, and perhaps don’t have
access to a mentor or ...
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Southern African Lapidary Stones to watch out for: Botswana Agates
Posted by Site Moderator Webmaster on Tuesday, June 25, 2019,
In :
Lapidary
Willie Visser
has had this Botswana agate for a number of years. Recently he decided it was time
that he took the plunge to cut it, and he was amazed to find it was the most
beautiful agate he had ever owned. He has called it “The Mona Visa”.
By coincidence it is
exactly 10 years since he cut open another special agate and found a fish. ...
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Zultanite - A relatively new gemstone from Turkey
Posted by Site Moderator Webmaster on Monday, June 24, 2019,
In :
Mineralogy
By Peter
Rosewarne
My
wife and I recently visited Istanbul for a few days on our way to Venice and
beyond. An 11-hour non-stop flight on Turkish Airways from Cape Town
International Airport got us there. Impressions of Istanbul were favourable;
interesting, friendly, good food, clean and safe. We stayed in the Old City and
did a lot of walking and had an obligatory tourist boat ride along the
Bosphorus (East meets West). We visited the Grand Bazaar, the largest covered
bazaar in the World with...
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Tanzanite
Posted by Site Moderator Webmaster on Monday, June 24, 2019,
In :
Faceting
Duncan Miller
A tanzanite was re-cut last month by Duncan. The original stone
was very lop-sided, with a shallow pavilion on one side, so there was
considerable weight loss. The girdle is deliberately thick to retain weight and
keep the finished stone over 5 ct.
14,6 × 11,1 × 7,3
mm; 8,67
ct before re-cutting
12,5 × 10,5 × 6,7 mm; 5,39 ct after re-cutting ...
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HYBRID DOPPING WITH WAX AND CYANOACRYLATE GLUE
Posted by Site Moderator Webmaster on Monday, June 24, 2019,
In :
Faceting
Duncan Miller
Initial dopping requires a flat surface on your rough. Prepare a
flat dop with a blob of hot wax on it and in the transfer fixture push this
against another flat dop face to form a layer of wax a few millimetres thick.
You can build this up with several layers if the stone you are going to cut is
very heat sensitive. Clean the flat on your rough with alcohol. When the wax is
cold, apply a small drop of cyanoacrylate glue (CA), position the rough on the
dop quickly, and let the gl...
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Ye Olde English Spar Boxes – a Hobby Revived!
Posted by Site Moderator Webmaster on Monday, June 24, 2019,
In :
Mineralogy
Lesley AndrewsDuring the
nineteenth and early twentieth centuries a popular pastime among the mining population
of Northern England was the construction of spar boxes. These were used to
decorate their homes, and also to sell to make some extra money. Spar boxes
were made up of various crystals (spar is the old name for a crystalline
mineral) which were collected by the miners working in the lead and iron mines
of the north Pennines and Lakeland areas.
My first
encounter with spar boxes in 200...
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Rhodochrosites
Posted by Site Moderator Webmaster on Friday, May 24, 2019,
In :
Faceting
Duncan
Miller
These are the rhodochrosites
(presumably from Hotazel) that I have been faceting, on and off, for the past
two months. The
‘pink’ stones (on the left) are 0,65 ct; 0,68 ct; 1,46 ct; and 0,96 ct.
The ‘red’ stones (on the right) are 1,39 ct; 1,66 ct; and 1,71 ct. The rough
was acquired more than twenty years ago as a small batch of broken and
half-finished stones. A recent article about faceted rhodochrosite in The Journal of Gemmology inspired me to
try to resurrect them...
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WHO CUT THAT STONE, OR WHAT IS A GEM CUTTER WORTH?
Posted by Site Moderator Webmaster on Friday, May 24, 2019,
In :
Faceting
Duncan Miller
The
photograph here is of a magnificent 164,11 ct spodumene (variety kunzite) in
the collection of the Smithsonian Institution, USA (https://geogallery.si.edu/10002906/spodumene-var-kunzite).
The
accompanying text credits the mine at which it was found (in 2010 at the
Oceanview Mine in Pala, California), the funds with which it was acquired
(Tiffany & Co. Foundation endowment in 2012), and the photographer (Greg
Polley). So who cut this stone? This is like acknowledging the ar...
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FACETIPS A simple Emerald Cut
Posted by Site Moderator Webmaster on Thursday, May 9, 2019,
In :
Faceting
Duncan
Miller
The Emerald
Cut is not a meetpoint design so cutting stones with repeatable proportions and
facet widths involves guesswork. The following sequence for cutting pavilion
and crown avoids most of the guesswork and enables you to cut pairs or sets of
matched stones. This sequence is modified from FACET DESIGN Vol. 4 by Robert
Long & Norman Steel, in turn based partly on FACETING FOR AMATEURS by Glenn
& Martha Vargas. This example uses 5° steps for the three pavilion tiers,
but you ...
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WHAT IS A PSEUDOMORPH, AN EPIMORPH OR A PARAMORPH?
Posted by Site Moderator Webmaster on Thursday, May 9, 2019,
According
to https://en.wikipedia.org/wiki/Pseudomorph:
“In mineralogy, a pseudomorph is
a mineral or mineral compound that
appears in an atypical form (crystal system),
resulting from a substitution process in which the appearance and dimensions
remain constant, but the original mineral is replaced by another. The name
literally means "false form". Terminology for pseudomorphs is "replacer after original", as in brookite after rutile.
A paramorph (also
called allomorph) is a mineral chan...
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Phlogging a dead horse?
Posted by Site Moderator Webmaster on Thursday, May 9, 2019,
In :
Mineralogy
Jo WichtMany of
you are aware of my obsession with Blue Lace Agate, both from a lapidary point
of view and with stones from the mine, as well as my curiosity as to how the
mineral was possibly formed. Any new information that I come across, be it a
new specimen or comment, has to be investigated. Recently it was Marco
Campos-Venuti’s new book (Banded Agates: a genetic approach (2018) www.agatesandjaspers.com) which
set me off on the trail again because it has a chapter on Lace Agates. Marco...
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UNUSUAL CRYSTAL HABITS
By
Peter Rosewarne
Sifting
through my collection in order to catalogue and assess specimens more fully has
got me thinking more about some of their mineralogical and crystallographic
properties. Why are some examples of the same mineral one colour and others
another? Why are some stubby and others prismatic? What crystal system do they
each belong to? What is ilvaite or axinite or vivianite?
I’m
fascinated by the interesting habits that some minerals exhibit which in many
cases don’t see...
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FACETIP – QUARTZ
Posted by Site Moderator Webmaster on Thursday, February 21, 2019,
In :
Faceting
By
Duncan Miller
(This is a
follow-up to a previous article on faceting quartz, to be found with other
faceting articles on the club’s website http://ctminsoc.org.za/articles/category/Faceting.)
Every faceter
knows quartz, those great big glassy-looking chunks that seem to cry out to be
turned into doorknobs. Or pretty, golden ‘citrine’ that can cut brilliant
yellow stones. Or glowing, dark purple amethyst with seductive blue flashes,
dreamy rose quartz, or rutilated quartz with geom...
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SOME MUSINGS ON SELLING A MINERAL COLLECTION FROM SOUTH AFRICA
By Peter Rosewarne
Having
built-up a mineral collection the question arises, at some stage, as to what to
do with it looking to the future. Options include do nothing (and continue to
get enjoyment out of looking at and handling the specimens) and let someone
else worry about it when you’re gone (i.e. throw it away), give it away, donate
it to an institution (probably unwise in SA or anywhere probably), or sell it.
This article looks at some aspects of the pricing and selling process ba...
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FACETIP – TOPAZ
Posted by Site Moderator Webmaster on Saturday, January 19, 2019,
In :
Faceting
By
Duncan Miller
Topaz is a rather under-rated gemstone. This perhaps it due to the
fact that pure, colourless topaz is relatively plentiful. Much of it is
irradiated and then heat-treated to produce various intensities of bright blue.
Natural blue topaz tends to be much paler, although dark blue stones do occur
naturally. These are rare and hence more valuable. Natural topaz occurs in a
wide variety of colours, including light green, yellow, orange and pink. The
famous orangey-pink topaz fr...
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Two beached whales were spotted at Yzerfontein this past month, the first on 5th November and the second a few days later
Posted by Site Moderator Webmaster on Friday, November 23, 2018,
In :
Lapidary
And last week this fish appeared at Milnerton Lagoon
Grey
chalcedony and aragonite fish
This
is the same fish as above, but much prettier “when still alive”, and seen
under short wave UV light.
...
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"There’s treasure – I just have to find it"
Talking about
treasure hunting, let me tell you my story … It’s a tale of two parts.
I’ve always been the poster child
for the story told by Victor Borge: “if
there’s manure, there must be a pony.” It’s in my DNA.
Truth be told, my first real life
encounter with this approach was doomed.
To understand it better, you’d
have to know that back then Dinner, Bed and Breakfast at a swanky hotel cost
R40-00 and a full seafood buffet at the same hotel with all you could eat cos...
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FaceTips for December
Posted by Site Moderator Webmaster on Friday, November 23, 2018,
In :
Faceting
by Duncan Miller
This
month I will show you how to scale a GemCad diagram to a different L/W ratio.
This is very easy if the diagram is a fully meetpoint diagram, without a
preform. You note the initial L/W ratio from the Print Preview and then click
on Scale in the Edit menu. Here you check the X box because you want to change
the proportions in the X direction, then enter the appropriate numbers to
divide by the initial L/W ratio and to multiply by the one you want, and press
OK. The next me...
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FaceTips for November
Posted by Site Moderator Webmaster on Sunday, November 4, 2018,
In :
Faceting
By Duncan Miller
I started faceting in pre-GemCad days and found cutting ovals very
laborious. I would cut the girdles by eye, using various oval templates, and
placed the brilliant-style facets by eye too. Producing matching pairs was very
trying. The advent of meetpoint faceting and GemCad overcame all these
difficulties. Now there are lots of designs for ovals that are meetpoint,
requiring no preform, with the girdle outline evolving out of the cutting
sequence. You can access some of the...
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SEPTEMBER VISIT FROM CONSTANTIA WALDORF SCHOOL
Posted by Site Moderator Webmaster on Thursday, October 25, 2018,
The Waldorf School
asked us if they could visit the club again this year, and Claire Vaskys
organised the day for them. Thank you very much Claire.
Also a big
thank you to Rinda
who had kept all the little offcuts of stones, and dopped them in preparation
for the children to grind and polish, and who managed the workshop while they
were busy between machines.
Thank you
to Marsiglio
who brought his tools, raw and finished materials, and allowed the kids to take
his rock pick and smash it in...
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Geological Tour of the Rosh Pinah area
Posted by Site Moderator Webmaster on Tuesday, September 25, 2018,
Since we have never
fully explored the southern parts of Namibia before, we decided to head up to Namibia
a few days before the planned start of the FOSAGAMS Namibia 2018 tour to
explore the area. Heidi Naudé from the Pretoria Club put us in touch with
Gisela Hinder who owns the Rosh Pinah Geo Center and after some discussion with
Gisela on our interests, we pre-booked a guided geology tour with her. Our
first night in Namibia was spent camping along the Orange River, and a casual
walk acros... Continue reading ...
FaceTips for October
Posted by Site Moderator Webmaster on Tuesday, September 25, 2018,
In :
Faceting
By Duncan Miller
This
was another jeweller’s request. The setter had broken one of a matching pair of
blue-green stones, destined for earrings, bought by the client in India as
emeralds. They were apatite; but nevertheless the broken stone had to be
replaced to fit the already-made setting. Fortunately I had just one piece of
blue-green apatite that matched the colour. In order to produce a stone of the
same size and proportion I had to replicate the oval precisely. I could have
slapped fa...
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Southern African Lapidary Stones to watch out for
Posted by Site Moderator Webmaster on Tuesday, September 25, 2018,
In :
Lapidary
Verdite
Verdite
is a fairly soft South African stone found in the Barberton area. It is often
seen in African curio shops carved into animals. Its golden flecks distinguish
it from buddstone which is a much harder metamorphosed chert. Even more
distinctive is the “leopard rock” which is spotted serpentinite, also from that
area. JW
...
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FaceTips for September
Posted by Site Moderator Webmaster on Friday, August 24, 2018,
In :
Faceting
By Duncan Miller
Here
is a quick and easy oval with a standard 1:1.30 proportion. It has a fully
conical pavilion, so you can spin a conical preform, stopping just short of
producing a point. This means you don’t have to change angles and mast height
when cutting the sixteen pavilion facets, which saves time and avoids mistakes.
This is a fully meet-point design that doesn’t require a preform, so it would
be good for a beginner’s first oval. It doesn’t work well in quartz or beryl,
s...
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STAVOREN MICROMOUNT OUTING
Posted by Site Moderator Webmaster on Friday, August 24, 2018,
In :
Micromounting
Jako
Schonken
I arrived at OR Tambo airport on a cold winter’s Thursday morning,
hoping it wouldn’t rain. I hired a car and started driving in a northerly
direction, following my GPS to Marble Hall - a place I have only heard about in
the South African Micromount Society’s newsletters. I have been a member of the
South African Micromount Society (SAMS) for more than three years, but have
never been to their meetings or outings since they are based in Gauteng. Nor
have I ever met any of...
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FaceTips for August
Posted by Site Moderator Webmaster on Wednesday, July 25, 2018,
In :
Faceting
By Duncan Miller
Jewellers sometimes ask for the impossible, and it’s a challenge to try and oblige. This design was developed to cut the citrine for a dome-shaped ring. It had to be a ‘classical’ mixed cut with curved girdle lines to match the curve of the top of the ring. This design requires a preform to get the girdle facets the right size. The relative depth of the pavilion tiers affects the angles of the triangular corner facets, but these can b...
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Southern African Lapidary Stones to watch out for:
Posted by Site Moderator Webmaster on Wednesday, July 25, 2018,
In :
Lapidary
SODALITE
– this is generally sourced from Swartbooisdrif, near the Kunene River in
north-west Namibia. It has a Mohs hardness of between 5,5–6, is
generally fine grained, and works very well.
...
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Encouraging the Curiosity of the Next Generation
Posted by Site Moderator Webmaster on Wednesday, July 25, 2018,
Matt Lurie (5 years old), who lives in Johannesburg, was curious
as to the make-up of an (amethyst) Spirit quartz crystal so he bought one for
R10 in Johannesburg and de-jacketed/exfoliated/peeled it, to satisfy his
curiosity! The images below were taken by his dad (Robert’s son) Dan Lurie.
Continue reading ...
Zeitz Museum of Contemporary African Art
Posted by Site Moderator Webmaster on Thursday, May 24, 2018,
Once the grain silos
of Cape Town Harbour
Built in 1923 the old silos in Cape Town Harbour were used for
storing grain awaiting export, and were in operation until 1995. Today they
house a modern art gallery. Thanks to the generous sponsorship of Jochen Zeitz,
(former CEO of Puma) and the incredible architectural imagination of the Heatherwick
Design Studio, the building is now a magnificent place to visit. The old round
tubes of silo have been cut away in specific places to open up a central ...
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Faceting
Posted by Site Moderator Webmaster on Monday, May 7, 2018,
In :
Faceting
Here are two stones that Duncan Miller cut recently
from rough he bought two months ago at Open Day. The yellow citrine (from
Johann de Jongh) has only 58 facets, is 22 mm wide and weighs 37 ct. The design
is ‘Xephyr’ by Arya Akhavan (yes, with an ‘X’). The light green fluorite (rough
from Rob Smith), is the first one he has ever cut. It has even fewer facets,
only 36, is 15,5 mm wide and weighs 16,2 ct. The design is slightly modified
from ‘Six Shooter’ by the late Jeff Graham. ...
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Visit to Mineral Services and the Exhibition “Messengers From The Mantle”
Posted by Site Moderator Webmaster on Thursday, March 29, 2018,
By kind invitation
of Professor John Gurney, 25 club members visited Mineral Services on 24th
February to
see his exceptional exhibition “Messengers from the Mantle”. This irreplaceable collection of kimberlites was initially
created for the 35th International
Geological Congress at the Cape Town International Convention Centre in September
2016, and was displayed again at the 11th International Kimberlite Conference in
Gaborone, Botswana in Septembe...
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Field Trip to Yzerfontein
Posted by Site Moderator Webmaster on Thursday, March 29, 2018,
Faceting
Posted by Site Moderator Webmaster on Wednesday, January 17, 2018,
In :
Faceting
A
magnificent 63 carat sphalerite from Aliva in Spain (http://gem-sphalerite.com/) cut by Duncan Miller. The design is Marco Voltolini’s
“Superstarfish Dome 80”.
A unique type of blue-green garnet has entered the gem market. The garnets
reportedly come from a deposit near the border of Tanzania and Kenya. GIA’s
Carlsbad laboratory obtained a small parcel of blue-green rough material and
two faceted stones for examination. Unlike traditional blue-green garnets that
exhibit a colo...
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“Tripping” in Namibia
Posted by Site Moderator Webmaster on Friday, November 24, 2017,
The
word “tripping” can have two meanings: a tour or journey, or an unintentional slip,
blunder or happening. On this
occasion both senses of the word applied. Malcolm and his friends covered
a lot of ground and saw a wide variety of things when in Namibia, but not
without incident.
To start off with, by the time Australian Graham landed in Cape
Town, he had lost his passport, which necessitated a return to Johannesburg and
the Australian Consulate for a new one. He then flew from JHB...
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Faceting
Posted by Site Moderator Webmaster on Friday, November 24, 2017,
In :
Faceting
“Eye of the Storm” a faceting design created by Robert W.
Strickland on 12th September 2017, in honour of those who suffered
loss in the Caribbean hurricanes of 2017.
This design was first published in the United States
Faceters’ Guild newsletter of September 2017.
When photographed directly into the centre of the culet, all
the crown facets go dark, and the only light is in the “eye”, but viewed from
other angles, the stone ...
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THE POLARISCOPE, THE FACETER’S FRIEND
Posted by Site Moderator Webmaster on Saturday, September 23, 2017,
In :
Faceting
Duncan Miller
A
polariscope consists essentially of two polaroid filters, or a source of plane
polarised light and one polaroid filter. The source of polarised light can be a
white computer screen or even the sky, viewed at 90 degrees to the Sun. For the
filter, or analyser, you can use a sheet of polaroid, or a lens from a cheap
pair of 3D movie spectacles.
Let’s
start with a white computer flat screen. Even an older cell phone screen
without a plastic cover produces plane polarised ligh...
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9th September, 2017. The Jan Coetzee Quartz Crystal Reunion
About ten
intrepid Jan Coetzee crystals made it to the reunion, with two of 50 kg-plus
guys sending their apologies due to being overweight, along with a couple more
whose owner couldn’t provide transport on the day. One rare and seldom seen
fluorite (also from the same crystal pocket) came, and was much admired.
Malcolm Jackson gave a short presentation about the mine and its location, along
with photos taken by him and Jo of the Jan Coetzee mine dumps in recent years
and the remains of th...
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FACETING THE NAMIBIAN RARITIES
Posted by Site Moderator Webmaster on Thursday, August 24, 2017,
In :
Faceting
Duncan Miller
During the 1974/75 university holidays I was fortunate to work for
Sid Pieters in Windhoek for several months. It was a wonderful experience,
including seeing some of the most famous mineral specimens then coming out of
Tsumeb, but also to encounter some very special gem materials. Through Sid
Pieters’s generosity I returned home to Cape Town with a few small fragments of
jeremejevite from the original Namibian occurrence at Cape Cross and some
pieces of cuprite from Onganja t...
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Curling Stones
Posted by Site Moderator Webmaster on Thursday, August 24, 2017,
Lesley Andrews gave a most interesting
talk on Scottish curling stones. I thought curling was a Scottish winter game
played by village yokels. I was wrong! It has had Winter Olympic status since
1998. The game consists of two teams of four players each, with eight stones
between them, and the idea is to slide the stone, which turns, hence the name
curling, towards a target called a button. Rather like a game of bowls on ice.
The origin of the game goes back into obscurity, but the oldest know...
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FACETING FOR INCLUSIONS
Posted by Site Moderator Webmaster on Monday, July 24, 2017,
In :
Faceting
Duncan Miller
Inclusions in gemstones often are seen as just a nuisance by
faceters, who find themselves urged to buy only ‘clean’ rough. I suppose it is
a matter of taste, but inclusions that do not detract from the visual
appearance of a gemstone can aid in proving its authenticity. And some
inclusions definitely enhance the value and appearance of certain gems. A
visible ‘horse tail’ inclusion of asbestos fibres in Russian demantoid is
perhaps the most famous example of desirable ...
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Synthetics
Posted by Site Moderator Webmaster on Tuesday, June 27, 2017,
In :
Faceting
Duncan Miller
Synthetics are a wonderful source of relatively inexpensive
faceting rough, in a wide array of colours, some of them not available at all
in natural stones. On the whole, synthetic gem rough is predictable in its behaviour
and also enables the cutter to explore quirky cuts in larger sizes than would
be affordable in natural rough. And increasingly jewellers are setting well-cut
synthetics in precious metal jewellery. So dive in, and enjoy yourself.
The most commonly available ...
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New Barite Occurrence at Rosh Pinah Mine – Namibia
Posted by Site Moderator Webmaster on Tuesday, May 23, 2017,
Transparent to whitish barite mineralization was found in an
orogenic late phase leached fault zone. It seems that some of the barites are
pseudomorphs replaced by snow white baritocalcite. This replacement supposedly
took place at an even later phase when calcium-rich fluids migrated through the
formation. This theory is supported by the occurrence of floater quartz
crystals in a pocket where, on the one side, the quartz aggregates display the
luster of ‘bergkristall’ and are coated on t...
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The History behind the Mike Lurie Collection
Posted by Site Moderator Webmaster on Tuesday, May 23, 2017,
The
Lurie family lived in Bulawayo, Rhodesia/Zimbabwe, from 1951 to 1966. During
this time Robert’s late father, Mike, worked as a manufacturer’s
representative. His job took him by car all over Southern Rhodesia (Zimbabwe),
Northern Rhodesia (Zambia) and Nyasaland (Malawi). Every now and again Mike
would stop his car in the middle of the bush to take a break from the
difficult, long distance driving. He would often notice something shining, or
an agat...
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Working With Diamond
Posted by Site Moderator Webmaster on Tuesday, May 23, 2017,
In :
Faceting
Duncan Miller
No, this is not about polishing diamonds, which in
South Africa is illegal without a license, but about working with diamond grit
or paste. For the coloured stone gem cutter, diamond paste is easier to source
and to use. Loose grit and pastes are available in a range of mesh sizes, with
crushed natural diamond or synthetic diamond. Synthetic diamond is made as
single crystals and polycrystalline aggregates. The polycrystalline diamond
breaks down with use to produce finer parti...
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TOURMALINE
Posted by Site Moderator Webmaster on Tuesday, April 25, 2017,
In :
Faceting
Duncan Miller
Tourmaline can be temperamental. Rough tourmaline occurs in two
distinct shapes – globular nodules and elongated pencil-like crystals elongated
in the direction of the c-axis. The
globular nodules sometimes spall concentrically, like onions, and the pencils
sometime fracture transversely. This behaviour is difficult, if not impossible
to predict, although fine cracks in the ‘skin’ of tourmaline pencils is not a
good sign. The cracked skin must be removed by preforming or th...
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New Barite Occurrence at Rosh Pinah Mine – Namibia
Author: Gisela Hinder, Rosh Pinah Geo Center, Rosh Pinah, Namibia
e-mail: gisela.hinder007@gmail.com
Rosh Pinah Mine is situated in the southwest of Namibia about 80 km
east of Oranjemund. Rosh Pinah Mine became well known for its beautiful barites
when a massive pocket of yellow to orange barite crystals was opened in 1989.
It is said that these barites were the best ever found in Namibia.
In February 2017 new barite crystals were discovered at Rosh
Pinah. Yellowish, unfortunately smallish, ...
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GARNET
Posted by Site Moderator Webmaster on Saturday, March 25, 2017,
Duncan
Miller
Garnets are among the easiest gem materials to facet. They have no
distinct cleavage, although some crystals have a parting that causes them to
fracture into thin slabs. The rough often is in globular shapes, which is good
for weight recovery. When choosing rough, avoid being fooled by fake material.
Red glass is sometimes covered in adhering deceptive ‘grit’ to mimic natural
nodules. Illuminated from behind or the side with a torch, the characteristic
internal swirls and r...
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A Bit about Blue Lace Chalcedony
Jo Wicht
Blue
Lace “Agate” is found on the farm Ysterputs 254 (meaning iron holes) in
Namibia. The mine is located adjacent to the “Blinkpan” (shining shallow lake)
which can be seen to the west of the B1 highway about 80 km north of
Vioolsdrift and Noordoewer, which are the border towns on either side of the
Orange River between South African and Namibia.
Blue
lace is not a true agate, but a chalcedony (microcrystalline quartz) laid down
in a series of wavy bands, which gives it th...
Continue reading ...
The Beryl Family
Posted by Site Moderator Webmaster on Friday, February 24, 2017,
In :
Faceting
Duncan Miller
Many faceters recommend that beginners start with aquamarine. It
usually presents no problems in faceting or polishing, is relatively easy to
obtain, and in lighter colour it is not overwhelmingly expensive. Aquamarine is
the blue or blue-green gem variety of the mineral beryl, an aluminium beryllium
silicate. It occurs in elongated hexagonal barrel-shaped crystals. It is
dichroic, with the most intense colour when viewed along the length, the
so-called c-axis. This is a pity,
...
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Faceting and Polishing Quartz
Posted by Site Moderator Webmaster on Sunday, January 15, 2017,
In :
Faceting
Duncan Miller
This is the first of an intended series of articles
on faceting and polishing a variety of gemstones. I am
beginning with quartz because that is what most people start faceting when they
first take up the hobby. Quartz rough is inexpensive and readily available in a
wide range of colours. It is not necessarily the easiest material to polish,
but if a particular stone behaves badly it is no great loss to set it aside to
be tackled at a later date. You should try to select rough ...
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Playing With Stars
Posted by Site Moderator Webmaster on Wednesday, November 23, 2016,
In :
Faceting
I
cut off the end of a damaged Goboboseb quartz crystal because it had a deep
purple central inclusion at the one end, which I thought would make an
interesting stone to facet.
But then I
noticed that the end of the remaining piece had regular purple stripes
radiating from the centre to the points of the hexagonal crystal. So I cut off
another section of the crystal to the depth I hoped I would need for cutting a
gem.
I
first tried to find the middle of the purple star shape, and marked s...
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Who Knows Nigel?
Posted by Site Moderator Webmaster on Sunday, October 23, 2016,
In :
Lapidary
Not many people in our club
know Nigel Brown, but behind the scenes he must be one of our most productive
lapidaries, in and among all his other commitments. His website has been listed
in this newsletter’s advertisements for several months now (nigelbrownjadecarver.com).
When
I looked at it again recently I saw he had been busy producing jade kiwis so I
asked him for an update of his work. He sent us this:
“Little Spotted Kiwi
This little...
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THE C-AXIS, WHAT IT IS AND WHY IT IS USEFUL TO GEM CUTTERS
Posted by Site Moderator Webmaster on Friday, September 23, 2016,
In :
Faceting
by Duncan MillerAll crystals
fall into one of seven crystal systems, based on their symmetry. In crystal
drawings, by convention, the c-axis usually is orientated vertically, in the
plane of the paper. All crystals except those in the cubic (or isometric)
crystal system have a c-axis. Cubic system crystals, like diamond, garnet and
spinel, have no c-axis because all three crystallographic axes are necessarily
the same length. In the other crystal systems the c-axis can be longer or
shorter th...
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THE SECRET OF A GOOD POLISH – IS A GOOD PRE-POLISH
Posted by Site Moderator Webmaster on Sunday, August 28, 2016,
In :
Lapidary
In the bad
old days, one cut facets on a 600 mesh lap, followed by a 1200 mesh lap and
then went on to polish. The 1200 mesh leaves quite deep scratches, and on some
material produces ‘orange peel’, a mottled surface with alternating rough and
smooth patches. This makes polishing tedious. A pre-polishing step, with 3000
mesh or 8000 mesh diamond gets rid of the scratches and any orange peel. You
might think the additional step adds time to the process, but in practice it
speeds it up beca...
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Selecting Rough
Posted by Site Moderator Webmaster on Saturday, June 25, 2016,
In :
Faceting
By Duncan Miller
If you are
going to facet, you need to learn something about mineralogy because you need
to know what stones you should obtain, how their characteristics affect their
behaviour while you are cutting and polishing them, and how they affect the
optical properties of your finished gemstone. The easiest material for beginners to cut and polish is common red garnet. It
presents no problem with cleavage or orientation for colour, and generally
behaves itself well during ‘cutting...
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Skorpion Mine, Rosh Pinah, Namibia - some rare and recent minerals
Posted by Site Moderator Webmaster on Saturday, June 25, 2016,
By
Gisela Hinder, Rosh Pinah Geo Centre
The Skorpion non-sulphide zinc mine in southwestern Namibia has always
produced interesting and rare minerals. To name only a few amongst the great
variety of zinc carbonates, phosphates and silicates discovered at Skorpion,
the skorpionite, hemimorphite, smithsonite and tarbuttite crystals are probably
the best known. Nevertheless, Skorpion mine has an area where copper values in
the host rock are higher, and minerals like malachite, chrysocolla,
zincol...
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Azurite Suns: Mineral Masterpieces from Australia
Posted by Site Moderator Webmaster on Wednesday, May 25, 2016,
Reproduced with the permission of Eric Greene of Treasure Mountain
Mining
Azurite is a soft,
deep blue copper mineral produced by the oxidation weathering of copper ore
deposits. It is a favourite amongst mineral collectors because of its rich blue
colour and wide availability in a variety of forms and colour variations, from
sharp, lustrous brilliant dark blue crystals to thick, rich, colourful royal
blue coatings on matrix.
Azurite suns are a unique
form of azurite that has been found in ...
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Re-polishing a Table Facet
Posted by Site Moderator Webmaster on Wednesday, May 4, 2016,
In :
Faceting
Anyone
who re-polishes worn stones, or who tries to remove a scratch from a table facet,
will be familiar with a common problem. Some stones, in my experience
particularly tourmaline, appear to develop a resistant ‘skin’ during polishing,
which impedes the re-polishing process. The effect is that you cannot re-polish
the facet, which just slides over the lap, with your usual polishing
combination. I think it is due to work-hardening of a surface layer; but there
are other opinions about w... Continue reading ...
Water Splash Covers
Posted by Site Moderator Webmaster on Thursday, March 24, 2016,
In :
Faceting
To reduce water spray when facet cutting at high speed, use a splash guard cut from the lid of a cheap plastic bucket, or alternatively use a trimmed-down cake fruit mix bucket when cutting girdles on a Raytech faceting machine.
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Going Home
A 30 kg nugget of Onganja copper is returning home to Namibia for posterity.
The Onganja mining district is situated in Namibia about 80 km NE of Windhoek, near the town of Seeis. Copper and molybdenite ores were mined there for many years, but for mineral collectors Onganja was particularly famous for its cuprite and malachite specimens.
In very early times local Ovambos travelled up to 500 km south from their homeland to mine copper in the Onganja area. They smelted the copper ores (chalcocit...
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Photographing Minerals & Gemstones
Posted by Site Moderator Webmaster on Monday, November 23, 2015,
In :
Faceting
It is relatively easy to take acceptable photographs of mineral specimens. Five years ago I photographed my Riemvasmaak fluorite collection for illustrations for an article published in Lapis magazine (Miller, D. 2010. Die Fluorite von Riemvasmaak, Südafrika – ein Besuch vor Ort. Lapis Mineralien Magazin April: 38-44). These were taken with nothing more sophisticated than a cardboard box with cut-out windows covered with matt tracing paper in sunlight, and sloping black or white paper in...
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Cutting Cerussite
Posted by Site Moderator Webmaster on Tuesday, August 25, 2015,
In :
Faceting
17 mm square, 55 carat cerussite faceted by Duncan Miller from rough provided by Rockey Ollewagen
Cerussite is lead carbonate (PbCO3) and probably the best crystals come from Tsumeb. These can be large and glassy, usually clear, but sometimes grey, brown or red. It has a hardness of 3½; a specific gravity of 6,5; distinct cleavage in two directions; is very brittle and extremely heat sensitive. The refractive index is high, at 1,90 to 2,07; and the birefringence very strong. The dispersion is...
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An unconventional Way of pre-forming “Doorstops
Posted by Site Moderator Webmaster on Thursday, July 23, 2015,
In :
Faceting
I have an unfortunate tendency to cut “doorstops”, which in the faceting world means cutting a mighty big gem, such as the 50 carat amethyst shown here.
When a piece of rough asks to be cut into a gemstone, I always feel that I would like get the maximum-sized stone from the rough, regardless of a few inclusions, as they always add a bit of interest or a few additional flashes to the finished result.
BUT…….. cutting big pieces of quartz and not having any kind of pre-forming grinding wh...
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My new View of Mineral Specimens
Posted by Site Moderator Webmaster on Thursday, July 23, 2015,
by Dave Hawes
A few years ago I purchased a microscope from Rolf with the view of exploring my specimens to a greater depth. Like so many good intentions the microscope languished in a cupboard for a year or two before I found the time to put it to use and realise what I had been missing out on. Not only were there minerals in different habits, but also species that I did not know I had and also ones that I did not even recognise. It was a whole new fascinating world of discovery!
After a while...
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Collecting Mining Ornaments
A couple of years ago, I bought a small ornamental gold-panning
miner from a charity shop. As he was related to our hobby, I wanted to rescue
him from an unknown fate, and little did I know it then, but he was the start
of a new collecting hobby. Today, I have several mining ornaments, which were
shown at a “What’s Up?” exhibit at the June monthly meeting. They are rather
rare, and all have been bought cheaply from secondhand dealers. They are made
of metal, with two mounted on sliced a...
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Blood in the cracks?
Posted by Site Moderator Webmaster on Wednesday, June 24, 2015,
by Martine van der Westhuyzen
In the FOSAGAMS announcement of their coming
Vivo outing in July, I read that, amongst other stones, dragon stone can be
found at Vivo. I wondered what dragon stone could be, so I consulted our old friend
Google to find out. This yielded such a diverse set of responses that it took
me several hours to try to get to the bottom of the mystery. It included
references to dragon stone, dragon blood stone, bloodstone, etc. – but are
these all different kinds of stones...
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The Romance of the Stone
Posted by Site Moderator Webmaster on Friday, May 22, 2015,
In :
Lapidary
“The Romance of the Stone?!”
- excitement at having
found a special piece of rough that asks for faceting
- carefulness to get the right
design for the rough
- caution by previewing
the new design on GemCad first
- fear to start
new designs or try different types of stones
- bravery to just do
it
- patience
to remove the initial surplus rough and reach the centre point and
s...
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Skorpion Zinc mine – another new mineral discovered
By Gisela Hinder
The Skorpion Zinc deposit is a complex, non-sulphide zinc orebody situated in a paleo-channel fill overlying rocks of the Port Nolloth Zone of the Gariep Belt about 20 km north-west of the little mining town Rosh Pinah, Karas Region, Namibia.The Skorpion Zinc mine is the 8th largest Zinc Mine in the world and a world-class integrated mining and refinery operation. Skorpion Zinc's annual capacity is 150 000 tons of Special High Grade zinc.The zinc-oxide is mainly hosted by arko...
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AGM & Tsumeb
Posted by Site Moderator Webmaster on Thursday, March 26, 2015,
The March
Monthly Meeting was our Club’s Annual General Meeting, and, as proof that our
present Committee is doing a great job of work, they found themselves
unanimously voted into office again. Thus our Committee again consists of
Malcolm Jackson, Ken Coleman, Jo Wicht, Carol Coleman and Tracy Hannath.
Congratulations folks! Keep up the good work.
Then Richard
Harrison gave a talk on Tsumeb minerals. He recently graduated with a degree in
geology, and we are proud of our new whizz-kid. H...
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Volcanoes - a red hot love affair
Posted by Site Moderator Webmaster on Monday, February 23, 2015,
If you remember, last November, TVJ (with the aid of Malcolm and
his photos) gave us a very interesting talk on zeolite minerals. These minerals
are to be found in ancient lavas that flowed out millions of years ago from
volcanoes such as those at the Etendeka Plateau in Namibia or the Deccan
Trappes in India. Later such minerals as analcime, chabazite, heulandite, and
apophyllite were created by mineral rich solutions percolating through the
porous rock and filling the residual cavities, k...
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Sing in the New Year
Posted by Site Moderator Webmaster on Monday, February 23, 2015,
In :
Lapidary
André Bergh gave a talk and demonstration of what were described in
the last newsletter as “quartz singing bowls”. But as things turned out, the
bowls were made of frosted glass, in China. There was a selection in various
sizes, and they are tuned to musical notes. When tapped with a drumstick, or
using one in a stirring motion rubbing against...
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The Abandoned Fortress
Posted by Site Moderator Webmaster on Thursday, September 4, 2014,
Far
into the veld a few kilometers north of Steinkopf lies an “abandoned fortress”
- the haunt of eagles and buzzards by day and owls at night. In places is evidence
of a wide straight track now eroded into potholes and gulleys and overgrown
with scrubby bushes. It leads right to the foot of the cliffs in the valley
beneath the “fortress”. Th... Continue reading ...
My Collecting
Dave Hawes
I have always thought that there are two types of people in the
world, those who collect and those who don’t.
Those who don’t, often live in immaculate, almost antiseptic,
homes where nothing is out of place.
Those who collect can be divided into several groups: Those who
collect for business or academic reasons, it is their work. Those who collect
for the appreciation of all things natural, and who usually display a few
prized pieces on their mantelpiece. Those who collec...
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My Collecting
Rockey Ollewagen
My interest in crystals started
about fifteen years ago. I was just a regular IT guy, working in the corporate
environment, not having any idea what the crystal world was all about.
Then my
wife, Paula, arrived home one day with a quartz crystal which cost R70 at the
time. I couldn’...
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My Collecting, My Collection
Graham Harrison
The whole
thing started with a chance find of some lovely smoky quartz crystals while on
holiday in the Knysna area in 1973. I did however grow up on a farm near
Johannesburg, so these smoky quartz crystals led to me hunting for amethyst in
the Muldersdrift area and in later years spending many days at the old
limestone quarry outs...
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The Tigers Leave for the Jungle
Posted by Site Moderator Webmaster on Monday, September 23, 2013,
In :
Lapidary
Do you remember the Hout Bay tigers mentioned in our July newsletter? They are now finally free of their Namibian “African Dream” granite and leave for the “jungle” this week after seven months of dedicated work by Robin Kutiniyu. Each block originally weighed about 5 tons, and now is about 2,5 tons. The tigers’ bodies were worked to a high polish, and their stripes etched in freehand afterwards, with tigers eye cabochons inserted in their faces to help them see. Their bases will be...
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My Collecting, My Collection
Trevor Vaughn Jones
I began collecting minerals as a schoolboy, when I was given a piece of “copper pyrites”, and even earned by Boy Scout’s Naturalist Badge with a shoebox full of rocks. But my more serious collecting began in my late twenties, when Cape Town had a number of curio shops, all selling Tsumeb and Namibian minerals. They were common – but much harder to find then were South African minerals. I still have two of my earliest: a rhodochrosite and a manganite. I can remember ...
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My Collecting, My Collection
Peter Rosewarne
How It All BeganMy first exposure to the world of minerals and crystals was while taking geology ‘O’ and ‘A’ levels at school in Brighton, UK, in the late sixties. My interest was of a fairly general nature at that stage, although the seeds of mineral collecting were sown on some field trips, one to North Wales, where I remember being excited by picking up some pyrite and bornite specimens. Next stop was reading geology at Kingston University, London, where a firm inter...
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My Collecting, My Collection
My mineral collecting did not start out well. I dropped a prized calcite specimen and it broke. Thirty five years later I still regret it. My clumsiness put me off collecting minerals for twenty years. Evidently I was not up to looking after these treasures that grow in the dark. Instead, as an unconscious penance, I concentrated on faceting, which really is a matter of painstakingly transforming broken crystal fragments into reflective gems, giving them renewed sparkle and life.
But the hunt ...
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Hunting for Tigers in Hout Bay
Posted by Site Moderator Webmaster on Monday, June 24, 2013,
In :
Lapidary
Who would have thought there were tigers lurking in Hout Bay?
In amongst the warehouses of Mariners Wharf, surrounded by chunks of picture stone, granite, rose quartz, sodalite and ironstone, and with an all pervading smell of oily fish, you will find Robin and his tigers. This is a stone carver extraordinaire who brings an amazing sense of movement and reality to his work. His current project of life-size tigers creeping through the undergrowth is his biggest challenge to date.
I was first int...
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Fundamentals of Lapidary, Part 1, Introduction by Donald Clark
Posted by Site Moderator Webmaster on Saturday, June 1, 2013,
In :
Lapidary
From the International
Gem Society Reference Library
Introduction
... Lapidary is a hobby that is enjoyed by people
of all ages and circumstances. Unlike most hobbies, what you produce is
actually worth more than the labour you put into it. For many cutters, their
hobby becomes a part time, or full time profession.
... Gem cutting can be don...
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The Colours of Quartz
The latest issue of The Journal of Gemmology has an excellent article by Ulrich Henn and Rainer Schultz-Güttler called ‘Review of some current coloured quartz varieties’. For those who don’t have access to this journal, published by the Gemmological Association of Great Britain, this is a short summary to help you distinguish the different varieties.
Uncut amethyst crystal, prasiolite (11,5 ct), rock crystal (20,5 ct), amethyst (2,5 ct), citrine (natural?) (8 ct), citrine and rose quar...
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Jaspers - part 2
Nebula stone. To quote from the Nebula Stone website: “There are companies that are trying to capitalize on the popularity of our stone’s name (Nebula Stone) because they have learned it has become very popular around the World. Some unethical companies have intentionally sold Kambaba/Kambamba/Kabamba Jasper/Crocodile rock/Galaxyite from Madagascar and South Africa falsely calling them Nebula Stone. Kambaba Jasper is not Nebula Stone. Nebula Stone is an igneous stone (from within the Eart...
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Jaspers Galore
JASPER – THE HISTORY
The name jasper means "spotted or speckled stone", and is derived via Old French jaspre (variant of Anglo-Norman jaspe) and Latin iaspidem (nom. iaspis)) from Greek ἴασπις iaspis, (feminine noun) from a Semitic language (cf. Hebrew יושפה yushphah, Akkadian yashupu).
Green jasper was used to make bow drills in Mehrgarh between 4th and 5th millennium BC. Jasper is known to have been a favourite gem in the ancient world; its name can be traced back in Arabic, P...
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Mineral of the Month - Ruby Corundum
Ruby from Afghanistan Ruby from Musina, S.A.
Specimen size 2,7 cm x 1,2 cm Specimen 2,5 cm, crystal 0,5 cm
Macro of Ruby corundum from Poona ...
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Mineral of the Month - Quartz
We all think we know quartz, and can recognise it, but it has possibly greater variation than any other mineral. First, it is only one of several different silica minerals made of only silicon and oxygen, linked together in the proportions of two oxygen atoms per silicon atom, hence the chemical formula SiO2. The other minerals, with identical chemical composition are tridymite and cristobalite (both high temperature minerals) and coesite and stishovite (both high pressure minerals). There is...
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Mineral of the Month - Braunite
Braunite II, andradite garnet, ettringite Braunite II on andradite garnet
(Wessels mine) (Wessels mine
Braunite II crystal (2,7 cm x 1,4 cm) specimen (4,1 cm x 3,5 cm)
Crystal system: Tetragonal Hardness: 6-6,5
Density: 4.8 Streak: Black
Cleavage: Perfect Composition: silicate Mn...
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SPODUMENE
Crystal system: monoclinic Hardness: 6,5 - 7
Density: 3,2 Streak: White
Cleavage: Perfect Composition: silicate LiAlSi2O6
Spodumene is derived from the Greek word “spodoumenos”, which translates to “burnt to ash”, which refers to the ashy colour of early specimens. Spodumene is a relatively new mineral having been discovered in the last 300 years, and gem varieties have only been discovered in the last ...
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Anorthoclase Crystal, Mount Erebus, Antarctica
Mount Erebus, the second highest volcano in Antarctica with a summit elevation of 3,794 metres, is located on Ross Island, which is also home to three inactive volcanoes. Mount Erebus is part of the Pacific Ring of Fire, which includes over 160 active volcanoes.
Geology and VolcanologyThe mineral anorthoclase ((Na,K)AlSi3O8) is a crystalline solid solution in the alkali feldspar series, in which the sodium-aluminium silicate member exists in larger proportion. It typically consists of between ...
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Stromatolites - Living Representatives of the Most Ancient Organisms
Posted by Site Moderator Webmaster on Saturday, May 26, 2012,
The rocks in the hyper-saline waters of Lake Thetis, about 120 km north of Perth in Western Australia, are not quite what they seem. They are actually living things. Stromatolites are the oldest living life-forms on our planet.
They are formed through the activity of primitive unicellular organisms: cyanobacteria (blue-green algae) and other algae. These grow through sediment and sand, binding the sedimentary particles together, resulting in successive layers which, over a long period of time,... Continue reading ...
Mineral of the Month - Opal
Common
or potch opal, 6cm x 4cm Locality unknown
Opalised ammonite, 6,5 cm x 4,5 cm Madagascar
Crystal system: Amorphous
Hardness: 4,5 –
6,5
Density: 1.9 – 2.3
Streak: White
Cleavage: None
Composition: ...
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Mineral of the Month - Pink Diamond
An
Australian mining company says it has found a 12,76 carat pink diamond, the
largest rough pink diamond found in the country. The rare diamond was found at Rio
Tinto's Argyle diamond mine in Western Australia's East Kimberly region.
Estimated to be worth millions, it has been named the Argyle Pink Jubilee, and
is being cut and polished in Perth. It will be sold later this year after being
shown around the world, including in New York and... Continue reading ...
ICELAND SPAR - Did the Vikings Use It for Navigation?
Posted by Site Moderator Webmaster on Sunday, February 19, 2012,
by Eric Greene
Iceland spar is a clear, transparent, colorless
crystallized variety of calcite (calcium carbonate, CaCO3). Large pieces are
split along natural cleavage planes to form natural rhombs. Iceland spar is
probably best known for exhibiting the optical property of double refraction -
so, anything viewed through the crystal appears double. It has many uses, in
everything from precision optical instruments to LCD screens, and was even used
during WWII to make bombsights. The pe...
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Mineral of the month - Coronadite
We
are pleased to inform you that the mineral coronadite has just been identified
at the Rosh Pinah Zinc Mine for the first time.
It is a predominantly lead based mineral with the
formula Pb (Mn4+, Mn3+)8O16. It is monoclinic, with a
hardness of 4½-5, and a member of the Cryptomelane Group. Its morphology is
massive, with boytroidal crusts with a fibrous structure. It was first
identified as a mineral in 1904, and is named after Francisco Vasquez de
Coronado (ca. 1500-1554), the first Sp...
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Fruits of the earth - Opal Pineapples
There are some mineral specimens in this world that beggar belief and the opal pineapples from White Cliffs in Australia are amongst those. They are palm-sized clusters of radiating points, looking like some bizarre fruit and have been known since the beginning of the 20th century. Found only in the Cretaceous sediments of the White Cliffs opal field in New South Wales, they occurred in an area which has also produced opalised fossils of marine shells, pieces of wood, and even the occasional ...
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Into the Skorpion's Pit
Posted by Site Moderator Webmaster on Wednesday, December 14, 2011,
The Skorpion zinc mine lies 25 km north of the town of Rosh Pinah, on the main road to Aus. On entering the mine, one is immediately struck that the area is split into two distinct operations. The first is the chemical refining plant, a huge steel structure of conveyors, tanks, etc., that uses 25% of Namibia’s electricity. Tucked away at the back of the plant is the open pit where the ore is mined by huge double-storey tip trucks, bulldozers and front-end loaders.
This deposit was
first di...
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Mineral of the Month - ZINC ORES – SPHALERITE
The main ore types mined at Rosh Pinah are carbonate ore,
microquartzite ore, and arkose ore containing mainly the sulphide ore minerals
sphalerite (ZnS), galena (PbS), chalcopyrite (CuFeS2) and Pyrite (FeS).
Specimen grade sphalerite crystals are occasionally found as attractive dark
brown metallic euhedral cubes in vugs and quartz veins in this mine.
Photo. G Hinder
They can also occur as an adamantine lustre of
golden brown and even yellow green colour, but not at Rosh Pinah. These
crysta... Continue reading ...
Mineral of the Month - Jeremejevite
Crystal
system: Hexagonal Hardness: 6,5 – 7,5
Density: 3,28 – 3,31 Streak: White
Colour: Colourless,
white, yellowish, pale to dark blue
Cleavage: None
Occurrence: A rare late hydrothermal
mineral formed in granitic pegmatites.
Habitat: ...
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Mineral of the Month - Chrysoberyl
Crystal
system: Orthorhombic Hardness: 8,5
Density: 3,5 – 3,84 Streak: White
Colour: Various
shades of green, yellow, brownish to green black (can be raspberry-red under
incandescent light when chromium is present)
Cleavage: Distinct, imperfect
Occurrence: ...
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Mineral of the Month - Stilbite
NaCa2Al5Si13O36
14H2O, Hydrated sodium calcium aluminum silicate
At
one time heulandite and stilbite were considered to be identical minerals. After they were found to be two separate
species, in 1818, the name desmine ("a bundle") was proposed for
stilbite, and this name is still employed in Germany. The English name "stilbite" is from
the Greek stilbein = to shine, because of the pearly luster of the {010} faces.
Stilbite is a common and perhaps the
most popular zeolite mineral ...
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Mineral of the Month - Analcime
Goboboseb crystals showing crystal clear analcime – photos and specimens
PdB
NaAlSi2O6-H2O, Hydrated Sodium Aluminium Silicate
The name of the mineral comes from the Greek word analkis that means weak.
Analcime is a zeolite and occurs frequently in basalts and other basic
igneous rocks associated with other Zeolites.
Crystal system: triclinic (Pseudo-cubic)
The aluminosilicate framework of the crystal structure does not change
in topology at all. The reduction...
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Mineral of the Month - Cuprite
Crystal
system: Isometric Hardness: 3,5 - 4,0
Density: 6,15 average Streak: Red
Colour: Red to a deep red that can appear
almost black.
Cleavage: Is fair in four
directions forming octahedrons.
Occurrence: Oxidized
zone of co...
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Mineral of the Month - Galena
Crystal
system: Isometric Hardness: 2.5 – 3.0
Density: 7.5 average Streak: Lead-grey
Colour: Silver lead-grey
Cleavage: Perfect, parallel to
the faces of the cubic crystals
Occurrence: In vein deposits and irregular
pockets w...
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Mineral of the Month - Kutnohorite
Kutnohorite
from Wessels and N’Chwanning mines (KMF). Specimens and photos by – J de Jongh
Crystal system:
Trigonal Hardness: 3.5 - 4
Density: 3.11 average Cleavage: perfect
Streak: white
Colour: white, light brown,
light yellow, light...
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Mineral of the Month - Barite
Barite
from Rosh Pinah, Namibia. ± 20 cm X 13
cm X 13 cm Specimen and
photos – J de Jongh
Crystal
system: Orthorhombic Hardness: 2,5 - 3,5
Density: 4.5 average Cleavage: very good
Streak: white
Colour: Colourless,
white, blue, red, yellow, o...
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Mineral of the Month - Cerussite
Crystal system: Orthorhombic Hardness: 3 - 3,5
Density: 6,5 average Cleavage: good
Streak: white Colour: colourless. white, gray, blue,
and green
Colour:
Occurrence: Occurrence:
It is a lead carbonate mineral, usually found in the oxidized zones of lead ore
deposits. It is a ...
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Mineral of the Month - Azurite
Azurite
from Tsumeb, Namibia. Specimen and photo – J de Jongh
Crystal
system: Monoclinic Hardness: 3,5 - 4
Density: 3.83 average Cleavage: perfect
Streak: light blue Colour: blue to very dark blue.
Occurrence:
A secondary mineral found in the oxidized zones of copper-bearing ore
depo...
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Mineral of the Month - Mimetite
Mimetite from Tsumeb, Namibia. Specimens and photo by
– J de Jongh
Crystal
system: Hexagonal
Hardness: 3,5 - 4
Density: 7,1 – 7,24 Cleavage: Imperfect
Streak: White Colour:
White, yellow, orange, brown, red.
Occurrence: A secondary mineral found in the
oxidized zones of...
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Mineral of the Month - Schorl
SCHORL (TOURMALINE GROUP)
Schorl from Erongo, Namibia. Specimens and photo – J de
Jongh
Crystal system: trigonal Hardness: 7
Density: 3.1 - 3.25 Cleavage: None
Streak: white
Colour: black,
brownish ...
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Mineral of the Month - Orbicular Granite
Along with several other club members, TVJ has
always been curious about the strange formation of orbicular granite. He challenged Nick Norman as to whether there
was any information about this granite in his book Geological Journeys, when
Nick was at the club in July. Yes, there
was, and this is what it says: “have a look at the famous, rare orbicular
granite west of the village of Concordia. It’s a national monument, and one of just two known occurrences in South
Africa, and of only a h... Continue reading ...
Mineral of the Month - Diamond
What is it that makes a diamond so attractive, and probably more sought after than any other gem? It is very hard and durable; yes, being 10 on the Mohs scale. It facets beautifully, and has industrial uses as well simply featuring in the jewellery trade. Diamonds can also be found in a variety of colours, including black, brown, yellow, with pale blue, and then red, green, and even pure orange and violet, which are the most rare. Formed up to 150 km under the ground, millions of diamonds...
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Mineral of the Month - Hausmannite
Crystal system: Tetragonal Hardness: 5.5
Density: 4.7 - 4.84 Cleavage: Perfect
Streak: Brown Colour: Black metallic
Occurrence: Occurs mainly in high temperature hydrothermal veins and in contact metamorphic deposits.
Habitat: Crystals are pseudo octahedral up to 7,5 cm. Composition: Mn2+ Mn3+2 O4
Followi...
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Mineral of the Month - Vanadinite
Vanadinite belongs to the apatite group of phosphates and has the chemical formula Pb5(VO4)3Cl. It is one of the main industrial ores of the metal vanadium and a minor source of lead. It is an uncommon mineral, occurring as the result of chemical alterations to a pre-existing material. It is found in association with the lead sulfide, galena, as well as wulfenite, limonite, and barite. It was first discovered in 1801 in Mexico by the Spanish mineralogist Andres Manual del Rio, and was eventua...
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Pegmatites - Basic Info
Posted by Site Moderator Webmaster on Tuesday, May 11, 2010,
Pegmatites
are dike-like bodies of large grained igneous rock, formed by the slow
crystallization of highly volatile solutions, during the last phase of
solidifying deep-seated granite magmas. The name comes from the Greek word
“pegmos” meaning “coarse”, and refers to their large-sized crystals, which are
mainly feldspar, quartz and mica. Their origin begins when a huge mass of
molten magma intrudes upwards through cooler surrounding country rock, a name
given to all other rocks, whi...
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Blesberg – June 2009
Posted by Site Moderator Webmaster on Tuesday, May 11, 2010,
It was with much yawning that Brett and I piled into my parents’ car at 3 am on Good Friday, to begin our trek up to Swartkop Camp Site. One last goodbye to three extremely unhappy dogs, and we were on our way. We arrived in Springbok at ten, to meet up with the Harrisons at the Springbok Lodge for breakfast, and then a short side trip to Steinkopf to meet a new member, Fanie, and bring him with us for the weekend. On arrival at Swartkop we set up camp, and then spent the rest of the day pa...
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Old Cape Town Mines
Posted by Site Moderator Webmaster on Tuesday, May 11, 2010,
by Trevor Vaughan Jones
THE QUARRY ON SEAFORTH BEACH
One of the least known quarries of the Cape Peninsula, and not easy to spot, was worked on Seaforth beach in 1865, where granite was shaped on site to re-enforce the shaky foundation of Roman Rock lighthouse, built only a few years earlier in 1861. This well known False Bay “landmark” (if one may call it that) is South Africa’s only lighthouse built on a rock at sea, which becomes visible at low tides. It was quite an achievement to...
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Mineral of the Month – Epidote
Epidote is a hydrous calcium iron alumino-silicate of medium hardness, between 6 and 7 on Mohs’s scale, and found in distinctive yellowish-green (“pistachio”) tones that range to an almost black colour. It is a metamorphic mineral, named by Hauy in 1801 from a Greek word “epidosis” meaning “addition”, because it was found to be an additional new mineral, and not a variety of tourmaline which it sometimes resembles, and until then what it was thought to be. Its crystals are rath...
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