Tangdanite

tangdanite

bornite

enargite

brochantite

Images

Formula: Ca₂Cu₉(AsO₄)₄(SO₄)_0.5(OH)₉.9H₂O
Arsenate sulphate
Crystal System: Monoclinic
Specific gravity: 3.22 measured, 3.32 calculated for the empirical formula
Hardness: 2 to 2½
Streak: Light green
Colour: Emerald-green
Luminescence: No fluorescence observed under UV
Environments

Hydrothermal environments

Tangdanite is a relatively new mineral, approved in 2012.

Localities

At the type locality, the Tangdan Mine, Dongchuan Cu ore field, Dongchuan District, Kunming, Yunnan, China, tangdanite is found in the oxidised zone of an arsenic-bearing copper sulphide deposit and is clearly of supergene origin. Associated minerals are chalcopyrite, bornite, chalcocite, covellite, tennantite, enargite, cuprite, malachite, azurite, copper and brochantite. Crystals form radiating or foliated aggregates of flattened, flaky crystals up to 3 mm in size. Tangdanite is emerald-green with a light green streak, translucent and with a pearly to silky lustre. It is sectile with perfect cleavage, although neither parting nor fracture was observed (MM 78.3.559-569).
Tangdanite from the Tangdan Mine - Image

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