Typomorphism of Minerals

the phenomenon of genetic conditioning of the characteristic properties and features of minerals. The typomorphic properties and features of minerals directly characterize the conditions of formation (and thus may serve as geothermometers and geobarometers) as well as distinctive features of the mineral-forming medium (variations in the alkalinity or acidity of the medium, in the partial pressure of gases, or in the composition of solutions or melts).

Typomorphic properties include morphological features of mineral segregations (crystal habit, formation of twinned crystals, and the nature of aggregates), variations in the chemical composition of a mineral and the admixture of contained isomorphic minerals, variations in the isotopic composition of constituent elements (Pb, S, O, and C are especially important), certain physical properties (density, microhardness, reflectance, luminescence, and electrical and magnetic properties), and structural features (degree of orderliness of mineral structures and differences in the structures of polytypes).

Much interest focuses on research on the typomorphism of minerals that are formed over a wide range of temperatures and pressures and that are present in different stages of deposit formation. Mineral typomorphism is used to solve numerous practical problems—in evaluating the degree of ore content of rocks, in prospecting for certain types of ore deposits, in determining the commercial value of ores, and in searching for concealed ore bodies.

The concept of mineral typomorphism in its modern sense was introduced by A. E. Fersman in 1931.