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Formula: Ca5(AsO4)2(AsO3OH)2(H2O)7
Arsenate
Crystal System: Triclinic
Specific gravity: 2.92 measured, 2.922 calculated
Hardness: 1½
Streak: White
Colour: Colourless to white
Luminescence: No fluorescence under long or short wave UV
Common impurities: Mg,Na,S
Environments
Jeankempite is a relatively new mineral, approved in 2018 and to date (May 2022) reported only from the type
locality.
Localities
At the type locality, the Mohawk mine, Mohawk, Keweenaw county, Michigan, USA, jeankempite was discovered
amongst coatings of arsenate minerals on oxidised
copper arsenides. It occurs as
lamellar bundles of colourless to white plates up to 1 mm wide and is visually indistinguishable from
guérinite, with which it forms intergrowths. It is suggested that
jeankempite formed due to dehydration of preexisting guérinite.
Jeankempite occurs as tabular crystals, intergrown with guérinite,
and as a secondary phase on "mohawkite" (a mixture of
algodonite, copper,
domeykite and paxite) and
calcite. Associated minerals include
algodonite, annabergite,
calcite, copper,
dolomite, domeykite,
guérinite, lavendulan and
rauenthalite
(MM 84.959-969, Mindat).
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