DIGGING OUT DUMORTIERITE

September 26, 2020

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 cupboard that had lovely blue patches in the rock. I bought it on a FOSAGAMS field trip to Griquatown many years ago. Piet of Earth Treasures had obviously cut out a core for a sphere and the remainder was left on the junk pile in his stone yard. Philip Alp had his eye on the offcut too, but graciously allowed me to buy it. I’ve dug it out and asked a couple of mineral friends what it might be, but neither are dead certain. I searched Mindat and wondered if it came from the dumortierite deposit on the farm Etemba in the Erongo region of Namibia. Mindat has a photo of a very small piece of rock. That seems the most likely – can anyone verify this, send more photos, or by a remote chance have the finished sphere from this chunk? According to the MinRec of September 2006, there was dumortierite at Etemba and in 1957 it yielded seven tons of material – that was 63 years ago!

Then I remembered I had a piece from Mozambique that came from the late Freddy de Jager. Where was that specimen? On hands and knees and half under the dining room table, I dug it out from dusty oddments at the floor level of my blue lace agate display shelves. The rock is nicely sawn at one end and shows the colour well. 

Mmmm… long ago I went on a club field trip to the Kenhardt/Kakamas area and we visited a dumortierite deposit on the N'Rougas Suid farm. It has been declared a National Monument/Provincial Heritage site as it is so unique. The farm owner allowed us to take one piece each from the furthest outlying areas of the deposit where it was outside the protective fence. Where was my bit now?  …… ah, in the rockery on the front porch. I dug it out too.  I remember John Landon made the farmer a sphere of that same dumortierite as a thank-you gift.



With my cutting and polishing complications now happily over, it has made me realise just how much “from troubles of the world, I turn to ‘rocks’, beautiful ‘eternal’ things…” (with apologies to FW Harvey).   JW

Here are photos of my pieces - now cleaned, worked, and polished, to show their true blue.  

    

From N’Rougas Suid - before    FOV 150 mm    From N’Rougas Suid – after        From Mozambique


Etemba farm, Namibia – Before                                    After - FOV 180 mm
 

LAZURITE – A TUCSON STORY

September 26, 2020

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

September 25, 2020

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

August 24, 2020
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

August 23, 2020

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

July 27, 2020

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

July 27, 2020
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

July 27, 2020

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

June 25, 2020

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

June 25, 2020

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...

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