Malladrite

malladrite

avogadrite

hieratite

ferruccite

Images

Formula: Na2SiF6
Halide
Crystal System: Trigonal
Specific gravity: 2.714 measured, 2.756 calculated
Hardness: 3
Colour: Pale rose, colourless, white
Solubility: Slightly soluble in cold water, slightly more so in hot water
Environments

Volcanic sublimate

Localities

At the type locality, Mount Vesuvius, Somma-Vesuvius Complex, Naples, Campania, Italy, malladrite is found as minute hexagonal prisms sometimes terminated by the pyramid, associated with salammoniac, avogadrite, hieratite, ferruccite and sassolite (AM 12.379-380, HOM).

At La Fossa crater, Vulcano Island, Lipari, Eolie Islands, Metropolitan City of Messina, Sicily, Italy, barberiite occurs as a fumarolic encrustation. Associated minerals include sulphur, malladrite, realgar, salammoniac, cannizzarite, galenobismutite and bismuthinite (AM 79.381-384).

At the Tolbachik volcano, Kamchatka Krai, Russia, malladrite occurs in an open fissure at the edge of a northern crater of the Large Tolbachik Fissure Eruption, and constitutes up to 19 wt% of white and brownish white exhalation crusts of gypsum, possibly anhydrite, and minor unidentified complex fluorides. Malladrite was found in 1985, when the walls of the fissure were at 60oC and temperatures of the fumarolic gases were less than 100oC. In 1988 and 1989, when temperatures were higher, the amount of malladrite decreased in the exhalations (AM 82.1041).

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