X-RAY STUDY OF KENNEDYITE

Abstract

We experimentally studied the solubility of titanium in a basalt melt at 1200° to 1300° C both in air (pO 2 = 0.21) and in a helium atmosphere. In the latter case, we determined the partial pressure of oxygen which, depending on temperature, ranged from 10 -8.5 to 10 -10.2 atm. The end products of our experiments were homogeneous silicate glass and crystalline phases, both oxide and silicate. The silicate phase was plagioclase, which was not observed at 1300° C. Oxide phases were present at all experimental temperatures, as titaniferous hematite, rutile and kennedyite. Whereas titaniferous hematite and rutile are widespread phases, kennedyite is rare. Thus, we have for the first time studied a set of synthetic kennedyite samples and shown that the cations incorporated into type-I octahedra are Fe 2+, Mg 2+, Fe 3+, Al 3+, and Ti 4+. Type-II octahedra probably are filled by Ti 4+ along. A characteristic feature of kennedyite is heterovalent isomorphism according to the scheme 2Me 3+ → Me 2+ + + Me 4+. Its unit cell parameters depend on the average ionic radius of cations the filling type-I octahedra.