Images
Formula: Ca(Ca,Mn)(SiO3OH)(OH)
Unclassified silicate, forms a series with olmiite,
manganese-bearing mineral
Crystal System: Orthorhombic
Specific gravity: 2.91 measured, 2.9 calculated
Hardness: 5
Streak: White
Colour: Colourless, milky white, pink-white
Common impurities: Fe,Mg,H2O
Environments
Localities
At the type locality, the Wessels Mine, Hotazel, Kalahari manganese field, Northern Cape, South Africa, poldervaartite occurs
in a pocket in massive braunite-hausmannite in
association with henritermierite and
calcite, and coated with bultfonteinite and
hematite
(AM 78.1082-1087, Dana).
At this locality hydrothermal alteration of the primary
manganese ore produced a wealth of well-crystallised minerals
(Mindat).
Poldervaartite from the Wessles Mine -
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Poldervaartite has been erroneously reported from N'Chwaning II Mine, N'Chwaning Mines, Kuruman, Kalahari
manganese field,
Northern Cape, South Africa, but all the specimens reported as poldervaartite are now believed to be
olmiite
(Mindat).
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