SturmaniteSome minerals only form in geologically uncommon…

Sturmanite

Some minerals only form in geologically uncommon events, and this pretty but complex borosulphate is one of them. Usually yellow to amber, it forms as attractive prisms with hexagonal cross sections. It is a member of the Ettringite group of minerals (see http://bit.ly/2wOt81R), and was named after an ex Associate Curator of Mineralogy at the Royal Ontario Museum, being a relatively recent discovery (1983). The two known sources are several mines in the Kalahari Manganese Field of South Africa (sharing a geological origin) and near Lakargi Mountain in Russia. It is a secondary mineral, formed by alteration of primary ore deposits during metamorphism, precipitating within cavities in the ore body from hydrothermal solutions. Too soft for jewellery use (2.5 on Mohs scale), crystals are usually small and hence only rarely faceted. Separating it from Ettringite requires lab analysis, which was performed in the case of this 3.6 × 3 × 2.6 cm specimen from the N’Chwaning 2 mine in South Africa.

Loz

Image credit: Jordi Fabre, http://www.fabreminerals.com/

https://www.mindat.org/min-3817.html