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