FACETING THE NAMIBIAN RARITIES

August 24, 2017

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 to experiment with polishing. From the jeremejevite I managed to cut two tiny gemstones. The cuprite baffled me for years, and I stashed it.

The jeremejevite, apart from its small size, was very easy to cut and polish. I dopped it with ordinary faceters’ brown wax on my smallest dops, and cut the facets very gently on a 1200 mesh sintered lap. Polishing on tin/lead with Linde A slurry was quick. It behaves, and looks like, aquamarine. Many years later jeremejevite was discovered on Ameib ranch in the Erongo mountains and became more plentiful, although facetable pieces remained rare. A friend of mine approached me with a ‘large’ crystal with an equally large inclusion and asked if it could be cut into an acceptable gemstone. There was only one way to find out and that was to cut it. The result was very pleasing, with the curved central crack actually enhancing the interest of the stone. And it is a gigantic 2,34 carats! (Subsequently I read in The Journal of Gemmology of a unique 100 ct colourless jeremejevite gem from Sri Lanka, but I have my doubts.[1])

About a year ago Rockey Ollewagen gave me a lump of cerussite from Tsumeb to try to facet. Previously I had had some success in polishing a few cuprite gems for the late Sigri Barella, including a 100 ct oval, about which I don’t have any doubts. For this I used a home-made wax lap and Linde A, but it rounded the facet junctions quite noticeably and I didn’t dive into my own cuprite stash. But I took on the challenge of cutting the cerussite and polished it quite easily without too much facet rounding with Linde A on a wax lap given me by Rob Smith. This story I have told earlier in the Min Chat, but what I withheld is something I thought would make me look crazy if published. When I transferred the stone it cracked – audibly and visibly – and an entire corner threatened to break off. In mild despair I put it one side to let it and myself cool off. When I returned to the stone the crack had disappeared. I don’t believe in healing gemstones, but this one had healed itself! Recently I read in a description of faceting cerussite that this is a unique characteristic of this material,[2] so I am relieved not to be so crazy after all.

The recent visits to the club by Stuart Moir, who worked the Onjanga copper mine, stimulated my trying to polish cuprite again. I didn’t want to return to the wax lap, so imported a Lightside™ lap from Gearloose Lapidaries in the USA. After facet cutting on a 1200 sintered bronze lap and pre-polishing with 3000 mesh diamond paste on copper, I struggled to get a good polish with the Lightside using a Gearloose AlOx Battstik™ in a water slurry. Using WD-40 with the AlOx (crazy combination) worked a bit better. Better still was 100 000 mesh Diastik™ with WD-40 on the Lightside™. This produced an OK polish, but under 10× magnification under oblique lighting there was a haze of fine scratches. Not to be deterred in the quest for the perfect polish on cuprite, I imported another Lightside™ lap and Jon Rolfe (aka Gearloose) made up a special 200 000 mesh Diastik™ for me. This produced an even better polish, but very slowly as one might expect. The problem with this was that cleaning the WD-40 off the stone with an alcohol-dampened paper towel to inspect the facet sometimes scratched it and adjacent facets. The published hardness of cuprite is 3½–4, so even a grain of house dust (mainly quartz) could scratch it. I am still trying to get the reliable perfect polish on cuprite. Perhaps I am crazy after all.

 

Jeremejevite, rough and cut, from Mile 72, Namibia. The larger stone is 3 mm,

the smaller 2 mm in diameter and the smallest stone I have ever cut.



[1] Smith, C.P. 2014. A rare 100+ carat jeremejevite. The Journal of Gemmology 34(2):138-142.

 [2] (Faceting the Good the Bad and the Ugly in Rare Gems by John Rhoads

 

Curling Stones

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

July 24, 2017

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

June 27, 2017

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

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

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

May 23, 2017

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

April 25, 2017

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

March 25, 2017

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

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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