What is Xanthoconite?
Xanthoconite is a rare silver arsenic sulfosalt and the monoclinic dimorph of proustite, prized for warm red-orange colour and high metallic density.
Mineralogy and structure
Reference formula: Ag3AsS3. Xanthoconite is monoclinic with the ideal formula Ag3AsS3. COD 9007500 provides an exact structural reference. It is a dimorph of proustite, not a colour variety of that mineral. Xanthoconite is classified with sulfosalts and has monoclinic crystal symmetry. Typical hardness is 2–3 on the Mohs scale and specific gravity is approximately 5.4–5.6.
Colour, lustre and habit
Typical colours include red-orange, yellow-orange, red-brown, brown. The usual prismatic, granular, massive habit and adamantine, resinous lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Xanthoconite forms in or is associated with oxidised and low-temperature hydrothermal silver-arsenic veins. Important documented localities include Lengenbach in Switzerland, Freiberg in Germany, Imiter in Morocco, Bolivia and Mexico.
The warm-coloured dimorph of proustite
Xanthoconite is a high-interest micromount and cabinet mineral because its red-orange colour, silver chemistry and relationship to proustite create a clear collecting story.
Collecting and care
Soft and silver-bearing: protect from scratches, light and acids, keep dry, and avoid dust-producing work.
