Kumdykolite, an orthorhombic polymorph of albite, from the Kokchetav ultrahigh-pressure massif, Kazakhstan

Abstract

Kumdykolite, an orthorhombic polymorph of albite, has been identified for the first time by analytical electron microscopy. It occurs in association with diopside, quartz/cristobalite, phengite/phlogopite, an unidentified aluminosilicate, calcic amphibole, dolomite, calcite, or talc, as micrometer-scale mineral inclusions in omphacite of eclogite from the Kumdy Kol, Kokchetav ultrahigh-pressure massif in northern Kazakhstan. The unit-cell parameters of kumdykolite were determined to be a = 8.24(1) A, b = 8.68(1) A, and c = 4.84(1) A, V = 346.17 A3, and with Z = 2. The space group could be either P 2 nn or Pmnn, but is probably Pmnn . Kumdykolite is presumed to be a metastable phase formed at high temperatures followed by rapid cooling in the absence of water. It is further postulated that kumdykolite may have resulted from the interaction between infiltrated melt and omphacite when the Kokchetav massif was exhumed from mantle depths to the base of the crust.