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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
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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