Green crystals of the relatively new mineral nickeltalmessite (IMA 2008-051) from the type locality and one of the only two known localities worldwide. Nickeltalmessite in sharp crystals is very rare but this specimen has at least one of them. From: Ait Ahmane, Bou Azzer, South Sahara, Morocco. — Photo: David Hospital · CC BY-SA 4.0
Nickeltalmessite
Nickeltalmessite is an IMA-recognized mineral species in the arsenate class, with the chemical formula Ca₂Ni(AsO₄)₂·2H₂O.
It crystallizes in the triclinic crystal system. It is a member of the Fairfieldite structural group.
Key properties: Mohs hardness 4; specific gravity 3.72; White streak; Vitreous luster; optically biaxial.
IMA symbol Ntlm, IMA status: approved, named in 2008.
Secondary in the weathered zone of a hydrothermal arsenopyrite-glaucodot-cobaltite deposit.
It is found associated with Annabergite, nickelaustinite, pecoraite, calcite, a mineral of the chromite- manganochromite series.
Identifies the nickel-dominant analogue of talmessite.