Krieselite, from Tsumeb, Namibia — Photo: David Hospital - www.purple-sky-minerals.com · CC BY-SA 3.0
Krieselite
An aluminium germanate-hydroxide found at Tsumeb, first catalogued in 1994.
Intro adapted from Wikipedia (CC BY-SA).
Krieselite is an IMA-recognized mineral species in the halide class, with the chemical formula Al₂(GeO₄)F₂.
It crystallizes in the orthorhombic crystal system (space group Pnma). It is a member of the Topaz structural group.
Key properties: Mohs hardness 5.5–6.5; specific gravity 4.069; White streak; Greasy luster; refractive index 1.81; optically biaxial.
IMA symbol Kes, IMA status: approved, named in 2000.
From vugs in tennantite-chalcocite-galena-germanite ore in a complex polymetallic hydrothermal sulfide deposit.
It is found associated with Quartz, wulfenite, anglesite, graphite (Tsumeb mine); schneiderhöhnite, stottite (Tsumeb mine 29th level).
The mineral was named to honor Friedrich Wilhelm Kriesel who was the chief chemist at the Tsumeb mine laboratory around 1920.