Articles

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...

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...

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...

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...

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 ...

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 ...

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...