Talmessite
This rare arsenic mineral is born when hydrothermal vein deposits that have precipitated from hot fluids are altered by further fluids of different chemistry, transforming the primary minerals into secondary ones. Named after its type locality (where it was first discovered) in Iran it forms small prism shaped crystals or radiating aggregates, varying from colourless to pale green (if rich in nickel) or brown to pinkish purple (when cobalt rich), as in the 4.3 x 2.8 x 2.5 cm specimen from Morocco in the photos. With a Mohs hardness of 5, and larger crystals being very rare it is not often cut, something also best avoided for the faceter’s health since arsenic minerals are of course toxic.
Loz
Image credit: Rob Lavinsky/iRocks.com
https://www.mindat.org/min-3876.html
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