Duncan Miller

Reproduced by courtesy of the Natural History Museum of Los Angeles County

Every year, the International Mineralogical Association approves the names of many newly discovered minerals (http://nrmima.nrm.se//recentmin.htm). The requirements are stringent, involving analytical descriptions of both the chemistry and physical structure of any candidate new mineral. Most of these are microscropic and not display-worthy. But every now and then, a new mineral is discovered that not only is macroscopic but also of gem quality. Brazilianite is a well-known example, first thought to be chrysoberyl but later recognised as a completely new mineral species. Taaffeite, originally discovered as a cut gem looking similar to spinel, is another example.

In 2015, kyawthuite, with the composition Bi3+Sb5+O4, was approved by the IMA on the basis of a type specimen consisting of a single faceted gemstone of 1,61 carats (http://minerals.caltech.edu/manuscripts/2017/Kyawthuite/index.html). It was found as a waterworn crystal in alluvium at Mogok Township, Myanmar – a region renowned for its varied gemstones. Now the cut gemstone is in the collections of the Mineral Sciences Department, Natural History Museum of Los Angeles County, USA (https://www.mindat.org/min-46909.html).

As far as I can determine, for now this faceted gem is the only known specimen of kyawthuite, making it not only the rarest mineral but also the rarest gemstone. If mineralogical and gemmological history is anything to go by, this situation is not likely to last long. Either the name will be discredited by another study showing that it is structurally and chemically too similar to a known mineral species to warrant another name – as happened fairly recently to the former ‘marshallsussmanite’ from the Kalahari Manganese Field, now synonymous with schizolite – or more mineral specimens will be found, and perhaps more gems.

The photographs of kyawthuite are all reproduced courtesy of the Natural History Museum of Los Angeles County