THE KAIDUN METEORITE: AN ENSTATITE CHONDRITE FRAGMENT WITH UNUSUAL INCLUSIONS IN THE METAL

Abstract

A petrological and mineralogical description of fragment 01.3.06 of the polymict meteorite breccia Kaidun is presented. The fragment is classified with EH3-4. This is the third type of enstatite chondrite that was found in this unique meteorite. The fragment is rich in metal nodules, which can be subdivided into three textural types: (1) globular, (2) zoned, with massive cores and globular rims, and (3) having no internal structure. The sizes and compositions of kamacite globules in the nodules and kamacite grains in the matrix are identical. The nodules contain small, commonly less than 5 urn, inclusions of widely ranging compositions: SiO 2, albite glass, enstatite, roedderite, and a mixture of SiO 2 and Na2S2. This is the first known occurrence of a simple alkalimetal sulfide in nature. The inclusions may have formed by condensation of material on the surface of metal grains. The nodules resulted from the agglomeration of individual metal grains and the simultaneous préserva-, tion of condensâtes as inclusions. The processes of condensation and agglomeration of the metal grains were synchronous. The inclusions may have formed by the disequilibrium condensation of gas of solar composition or by equilibrium condensation of highly fractionated gas.