Formula: CuI
Normal halide, chlorargyrite group, forms a series with miersite
Specific gravity: 5.68
Hardness: 2½
Streak: yellow
Colour: Colourless to pale yellow when fresh, turns pink to dark brownish-red

Hydrothermal environments

Marshite is found with oxidised copper minerals (Webmin)

At the type locality, Broken Hill Proprietary Mine, Yancowinna county, New South Wales, Australia, marshite is a rare halide in the oxidised zone of a metamorphosed lead, zinc, and silver deposit, associated with copper, cuprite, cerussite, malachite and iron-manganese oxides (HOM, Mindat)'

At Chuquicamata,Chile, marshite occurs in the oxidised zone of a porphyry copper deposit, associated with atacamite, copper, tenorite, and gypsum. The marshite, with atacamite, lines fractures in the sericitised and kaolinised granodiorite. In this section of the mine, antlerite, otherwise the principal oxidised copper mineral at Chuquicamata, is not stable. The marshite crystals penetrate the atacamite and perch upon it. (AM 24.629-635, HOM).

At Loytosuo, Finland, marshite has been found in tills over a copper anomaly, introduced by brackish seawater (HOM).

At the Rubtsovskoe copper, zinc and lead deposit, Rudnyi Altai, Altai Krai, Russia, marshite has been found as a partial pseudomorph of an azurite nodule (FM OP2577).

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