Natural Bromides

a group of rare minerals related to the halogen compounds. The minerals known in nature are limited to the silver bromides, which crystallize in a cubic system. The structures are of the same type as rock salt. Pure silver bromide is the mineral bromyrite, with the chemical composition AgBr. Bromyrite’s theoretical composition is: Ag, 57.44 percent; Br, 42.56 percent. Other minerals—embolite, Ag(Cl,Br), and iodembolite (or iodobromite), Ag(Cl,Br,I)—are halogen compounds of silver in which Br is replaced to a considerable extent (up to 10-14 percent) by chlorine and iodine.

The physical properties of the minerals of this group are very close. The natural bromides form fine crystals with a cubic or octahedral habit and a bright, diamondlike luster; they also form yellow or yellowish-green granules. They are soft and partially plastic. Their hardness on the mineralogical scale is 2.0-2.5; density (in kg/m³), from 5,660 (embolite) to 6,350 (bromyrite). The natural bromides are found exclusively in oxidation zones of sulfide silver-containing deposits, which form in arid desert regions.