Tyrolite is an uncommon turquoise-blue or blue-green secondary hydrated carbonate mineral found in the oxidised zones of copper deposits, usually with arsenates and sulphates. It is named for its type locality near Schwaz, Tyrol, Austria, and has the chemical formula CaCu5(AsO4)2(CO3)(OH)4 · 6(H2O). It has a Mohs hardness of 1.5-2, and is transparent or translucent with a pale blue streak. Crystals are generally small, twinned, flattened pseudo-hexagonal aggregates. Radiated and dendritic forms may be seen, and crusts and druses are fairly common for this mineral. It may be confused with theisite and claraite, two other rare minerals.

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Image: Tyrolite from Mammoth Mine, Utah, USA. Source: mindat (c) Rob Lavinsky & irocks.com

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