bismutite

Bismutite is a naturally occurring mineral composed of bismuth oxycarbonate, with the chemical formula Bi2(CO3)O2. It is a secondary mineral, meaning it typically forms as a result of the weathering and alteration of primary bismuth minerals, such as bismuthinite. Bismutite is a relatively rare mineral and is often found in small quantities in the oxidized zones of hydrothermal bismuth deposits.

The mineral typically appears as earthy, powdery, or mammillary masses, often with a chalky texture. It can also occur as microscopic acicular crystals. The color of bismutite is generally white, pale yellow, or gray, although impurities can sometimes impart greenish or brownish hues. It is known for its softness, with a Mohs hardness of 2 to 2.5, and a specific gravity of around 6.8 to 6.9. Bismutite is insoluble in water but will react with dilute acids, releasing carbon dioxide.

While not a primary source of bismuth, bismutite can be a minor contributor to the overall bismuth supply. Historically, it has been of interest to mineral collectors due to its occurrence in association with other rare bismuth minerals. Its formation process highlights the geological conditions under which primary bismuth ores undergo oxidation and transformation in the upper levels of ore bodies.