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Formula: Al6(Se4+O3)3[SiO3(OH)](OH)9.10H2O
Selenite, a polyoxometallate
Crystal System: Orthorhombic
Specific gravity: 2.27 measured, 2.32 calculated for the empirical formula
Hardness: 2 to 2½
Streak: White
Colour: Colourless
Environments
Sedimentary environments
Hydrothermal environments
Petermegawite is a new mineral, approved in 2021 and to date (October 2023) reported only from the type
locality.
Localities
At the type locality, El Dragón mine, Porco Municipality, Antonio Quijarro Province, Potosí, Bolivia,
petermegawite was found associated with cobalt-bearing
krut′aite–penroseite
(matrix), chalcomenite,
clinochalcomenite (unapproved, but probably valid),
molybdomenite,
lepidocrocite, goethite,
ahlfeldite and calcite.
The mine exploited a telethermal deposit (a hydrothermal mineral deposit formed at shallow depth and relatively
low temperatures) consisting of a single selenide vein hosted in
sandstone and
shale. The major ore mineral is
krut′aite, which ranges in composition to
penroseite. Late-stage fluid, rich in
bismuth, lead and
mercury, resulted in the crystallisation of minerals such as
clausthalite, petrovicite,
watkinsonite, and the recently described minerals
eldragónite, grundmannite,
hansblockite,
cerromojonite and
nickeltyrrellite. Oxidation produced a wide range of
secondary
selenium-bearing minerals, such as
favreauite,
alfredopetrovite,
bernardevansite (dimorphous with
alfredopetrovite),
franksousaite, and the new mineral petermegawite.
Petermegawite occurs as aggregates of bladed or tabular crystals, with individual crystals up to 0.15 x 0.08
x 0.03 mm3
(CJMP 61.987-998).
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