bismite

Bismite is a mineral species in the oxide group with the chemical formula Bi2O3. It forms as a secondary mineral through the oxidation of bismuth-bearing minerals in ore deposits and hydrothermal environments. In hand specimens it is typically yellow to brown and may occur as small prismatic or tabular crystals, or as crusts and drusy coatings on host rocks. The mineral is usually opaque, with a resinous to earthy luster, and Mohs hardness around 3 to 4. Its relatively high density reflects its bismuth content.

Bismite occurs most often in oxidized zones of bismuth-rich ore bodies and is commonly found in association with other secondary oxide minerals and with native bismuth or bismuth minerals formed during weathering and alteration. It may form coatings on fracture surfaces or as euhedral to subhedral crystals in vuggy environments.

Bi2O3 exists in several polymorphs, and bismite is one recognized mineral form of this oxide. Another mineral form of Bi2O3 is valentinite; these two minerals share the same composition but differ in crystal structure. The study of bismite contributes to understanding the oxidation processes in bismuth-bearing mineral systems and helps in characterizing secondary parageneses in related ore deposits.

Notable localities worldwide have reported bismite, and it is of interest primarily to mineral collectors and researchers rather than as an ore commodity.