What is Zincrosasite?
Zincrosasite is a soft blue-green zinc copper carbonate from oxidised base-metal deposits, usually seen as earthy or botryoidal coatings related to rosasite-group chemistry.
Mineralogy and structure
Reference formula: (Zn,Cu)2(CO3)(OH)2. Zincrosasite is monoclinic in traditional descriptions, but its structure has been flagged for reinvestigation. The Guide keeps the useful field formula and deliberately shows no lattice until a trustworthy public structural model is available. Zincrosasite is classified with carbonates and has monoclinic crystal symmetry. Typical hardness is 1–2 on the Mohs scale and specific gravity is approximately 3.5–4.0.
Colour, lustre and habit
Typical colours include pale blue, green, white. The usual botryoidal, crusty, massive habit and dull, pearly, vitreous lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Zincrosasite forms in or is associated with secondary oxidation of copper-zinc sulfide ores and carbonate-rich mine environments. Important documented localities include Tsumeb in Namibia, Rudabánya in Hungary, Sardinia and other copper-zinc districts.
Blue-green oxidation colour without false precision
Zincrosasite is attractive as a mine-surface mineral, but its collector value depends on honest identification. A well-labelled blue-green crust is more desirable than an overconfident name attached to a look-alike.
Collecting and care
Soft and acid-sensitive: protect crusts, avoid soaking and abrasion, and do not grind or use acid tests on a collectible specimen.
