Tanzanite

June 24, 2019
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


 

HYBRID DOPPING WITH WAX AND CYANOACRYLATE GLUE

June 24, 2019

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!

June 24, 2019
Lesley Andrews

During 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

May 24, 2019

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?

May 24, 2019
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

May 9, 2019

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?

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.

paramorph (also called allomorph) is a mineral chan...


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Phlogging a dead horse?

May 9, 2019
Jo Wicht

Many 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

March 25, 2019

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

February 21, 2019

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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