Talmessite (Size 64 mm x 37 mm x 26 mm) Locality: Aghbar Mine (Arhbar Mine), Aghbar, Bou Azer District (Bou Azzer District), Tazenakht, Ouarzazate Province, Souss-Massa-Draâ Region, Morocco Original description: A mass of reddish brown crystals of cobaltoan Talmessite. JSS specimen and photo. — Photo: John Sobolewski (JSS) · CC BY 3.0
Talmessite
A hydrated calcium-magnesium arsenate with cobalt and nickel, named for Iran's Talmessi mine.
Intro adapted from Wikipedia (CC BY-SA).
Talmessite is an IMA-recognized mineral species in the arsenate class, with the chemical formula Ca₂Mg(AsO₄)₂·2H₂O.
It crystallizes in the triclinic crystal system (space group P-1). It is a member of the Fairfieldite structural group.
Key properties: Mohs hardness 5; specific gravity 3.421; [Vitreous] luster; refractive index 1.685; optically biaxial.
IMA symbol Tlm, IMA status: approved, named in 1960.
A rare secondary species formed typically in the oxidized zone of some hydrothermal mineral deposits, an alteration product of realgar, orpiment, or Cu–Ni arsenides.
It is found associated with Gaitite, erythrite, annabergite, picropharmacolite, pharmacolite, austinite, fluorite, barite, aragonite, calcite, dolomite.
The name refers to the Talmessi mine, Iran, in which the mineral was first found.