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Formula: Ag4Pb20(Sb,As)24S58
Sulphosalt, antimony- and arsenic-
bearing mineral
Crystal System: Monoclinic
Specific gravity: 5.747 calculated for the ideal formula
Hardness: 3 to 3½
Streak: Black
Colour: Black
Environments
Metamorphic environments
Hydrothermal environments
Parasterryite is a relatively new mineral, approved in 2010 and to date (July 2024) reported only from the
type locality.
Localities
The type locality, the Pollone Mine, Valdicastello Carducci, Pietrasanta, Lucca Province, Tuscany, Italy, was
exploited in the Middle Ages for silver-bearing
galena, and in the 20th century for
baryte.
In 2010 parasterryite and sterryite were collected independently
in vugs within
baryte–quartz veins embedded in
baryte–pyrite lenses. An overgrowth
of minute yellow-green crystals of sphalerite was observed on the
sterryite needles, but parasterryite is free of any sulphide or
sulphosalt. Acanthite,
famatinite,
geocronite–jordanite,
pyrargyrite–proustite,
antimony-rich rathite,
tetrahedrite and
xanthoconite were also identified in the same occurrence.
Owyheeite and a
boulangerite-like sulphosalt have been found in this kind of
occurrence, but they were not identified in the samples studied.
Boulangerite was identified in
quartz veins embedded in the country rocks, as acicular to prismatic
crystals, up to several cm in length.
Parasterryite occurs as metallic black needles striated along their elongation, up to several mm in length
and 0.2 to 0.3 mm thick
(CM 49.2.623-638).
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