any of a group of chemical elements (Rb, Cd, Cs, Sc, Ga, In, TI, Ge, Hf, V, Se, Te, Re) encountered in nature chiefly as admixtures in various minerals and incidentally extracted from the ores of other metals or useful minerals (coals, salts, phosphorites). Dispersed elements can enter other minerals as isomorphic replacements of the main element (for example, hafnium in zirconium minerals), as microminerals detectable only with the help of a microprobe (tellurides in pyrite), and as admixtures absorbed by the surface of earthy (amorphous) minerals (vanadium in montmorillonite, selenium in limonite). They can also enter minerals through the formation of organometallic compounds (in coals) and through positioning at defect sites in the crystal lattice. As a rule, they do not form independent minerals, even at relatively high concentrations in the earth’s crust. Only in special cases are dispersed elements (Se, TI, Ge, V, Se, Te, and Cd) able to form characteristic minerals of their own.
Whether dispersed elements are dispersed among other elements or form minerals of their own is governed largely by the ratio in natural processes of the concentration of dispersed elements to that of their more widely disseminated geochemical analogues. For example, in abyssal zones, cadmium, a geochemical analogue of zinc, is always dispersed in zinc minerals, from which it is also extracted. In the oxidized zone, however, Cd and Zn separate; Zn is carried away and Cd accumulates in its own compounds.
REFERENCESGeokhimiia redkikh elementov v izverzhennykh gornykh porodakh (collection of articles). Moscow, 1964.
Ivanov, V. V. Geokhimiia rasseiannykh elementov, Ga, Ge, Gd, In, Tl v gidrotermal’nykh mestorozhdeniiakh. Moscow, 1966.
V. V. SHCHERBINA