What is Xanthiosite?
Xanthiosite is a rare nickel arsenate with a golden-yellow colour, known from oxidised arsenic-rich ore environments and specialist mineral collections.
Mineralogy and structure
Reference formula: Ni3(AsO4)2. Xanthiosite is monoclinic with the ideal formula Ni3(AsO4)2. COD 9007684 is used as an exact structural reference; an orthorhombic synthetic polymorph is known, so the natural mineral's symmetry must be stated clearly. Xanthiosite is classified with arsenates and has monoclinic crystal symmetry. Typical hardness is 4–4 on the Mohs scale and specific gravity is approximately 5.2–5.5.
Colour, lustre and habit
Typical colours include golden yellow, yellow, brownish yellow. The usual granular, massive, crusty habit and waxy, dull, earthy lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Xanthiosite forms in or is associated with oxidised nickel-arsenic veins, hydrothermal ore zones and secondary cavities. Important documented localities include Johanngeorgenstadt in Germany, Lavrion in Greece, Cornwall in England and other rare arsenate localities.
Golden colour in a rare nickel arsenate
Xanthiosite is a specialist collector mineral where unusual colour and chemistry matter more than crystal size. An authenticated locality and careful handling make a tiny specimen scientifically valuable.
Collecting and care
Nickel- and arsenic-bearing: keep sealed and dry, avoid dust, grinding and acid testing, and wash hands after handling.
