BISMUTHITE

bismuthite, a somewhat rare mineral, consisting of bismuth trisulphide, bi2s3. it crystallizes in the orthorhombic system and is isomorphous with stibnite (sb2s3), which it closely resembles in appearance. it forms loose interlacing aggregates of acicular crystals without terminal faces (only in a single instance has a terminated crystal been observed), or as masses with a foliated or fibrous structure. an important character is the perfect cleavage in one direction parallel to the length of the needles. the colour is lead-grey inclining to tin-white and often with a yellowish or iridescent tarnish. the hardness is 2; specific gravity 6.4-6.5. bismuthite occurs at several localities in cornwall and bolivia, often in association with native bismuth and tin-ores. other localities are known; for instance, brandy gill in caldbeck fells, cumberland, where with molybdenite and apatite it is embedded in white quartz. the mineral was known to a. cronstedt in 1758, and was named bismuthine by f.s. beudant in 1832. this name, which is also used in the forms bismuthite and bismuthinite, is rather unfortunate, since it is readily confused with bismite (bismuth oxide) and bismutite (basic bismuth carbonate), especially as the latter has also been used in the form bismuthite. the name bismuth-glance or bismutholamprite for the species under consideration is free from this objection. (l. j. s.)