Anhydrous arsenate containing hydroxyl, herderite group
Specific gravity: 3.4
Colour: Colourless, white, grey, dark grey-brown, brownish black, green, pink
Bergslagite is a rare arsenate.
At Sailauf, Germany, bergslagite occurs in rhyolite associated with hematite and muscovite.
At the type locality, Långban, Värmland, Sweden, bergslagite occurs as aggregates of elongated crystals in thin veins in fine-grained hematite ore, found on mine dumps from a metamorphosed iron-manganese orebody. It is associated with tilasite, diopside variety schefferite, manganberzeliite, svabite, baryte and calcite.
Common impurities: Si
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