Formula: K3Cu7Fe3+O4(AsO4)4
Anhydrous arsenate
Crystal System: Monoclinic
Specific gravity: 4.39 calculated
Hardness: 4
Streak: Dark green with an olive hue
Colour: Black
Common impurities: Zn


Melanarsite is a relatively new mineral, approved in 2014 and to date (January 2024) reported only from the type locality.


At the type locality, the Arsenatnaya fumarole, Second scoria cone, Northern Breakthrough, Great Fissure eruption, Tolbachik Volcanic field, Milkovsky District, Kamchatka Krai, Russia, specimens with melanarsite were collected at a depth of about 0.5 m below the surface and temperature of 360 to 380°C. Melanarsite was found in incrustations mainly consisting of arsenates, oxides and sulfates. It is believed that the melanarsite was deposited directly from the gas phase as a volcanic sublimate at temperatures not lower than 380°C. It occurs as well shaped or, more commonly, coarse crystals up to 0.1 mm, rarely up to 0.4 mm in size, separate or combined in clusters up to 1 mm across, rarely forming interrupted incrustations, up to 1 cm × 1 cm in area and up to 0.2 mm thick, covering basalt scoria. The most typical minerals associated intimately with melanarsite are dmisokolovite, shchurovskyite, bradaczekite, hematite, arsenic-bearing orthoclase, johillerite, arsmirandite, aphthitalite, tenorite, langbeinite, anhydrite, tilasite and fluorophlogopite. In some cases the melanarsite is associated closely with hatertite or pharmazincite (MM 80.5.855-867).

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