chromian

Chromian is an adjectival and nominal term used to denote substances in which chromium is a defining component. In mineralogy and geology, chromian minerals are those in which chromium substitutes for other cations in the crystal structure, or exists in notable amounts, giving characteristic colors and chemical behavior. The term is especially common for chromium-rich varieties within the garnet, pyroxene, and spinel groups. Well-known chromian minerals include uvarovite, a chromium-bearing garnet; chromian diopside; and chromian spinel. In spinels, Cr3+ commonly substitutes for Al3+ or Mg2+ in the spinel lattice, producing green to dark minerals.

In chemistry, chromian has historical usage to indicate chromium-containing species or salts and is not a formal oxidation-state descriptor in modern practice. Contemporary nomenclature generally specifies chromium’s oxidation state, such as chromium(III) oxide (Cr2O3) or chromate and dichromate anions CrO4^2- and Cr2O7^2-. The term may appear in older literature describing chromic salts or complexes and in descriptive mineralogy.

Chromium is a transition metal that occurs naturally in several rock-forming minerals, most notably chromite (FeCr2O4). The presence of chromium in minerals influences color, hardness, and stability. Chromian materials are of interest in geology, geochemistry, mineral exploration, and materials science due to their distinctive properties and occurrence in mantle- and crust-derived rocks.

See also chromium, chromite, chromian garnet, uvarovite, chromian diopside.