Unclassified silicate, forms a series with olmiite
Specific gravity: 2.91
Colour: Colourless, milky white, pink-white
Common impurities: Fe,Mg,H2O
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 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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