THE KAIDUN METEORITE - AN ENSTATITE CHOND RITE FRAGMENT WITH UNUSUAL INCLUSIONS IN THE METAL

A petrological and mineralogical description of fragment 01.3.06 of th e polymict meteorite breccia Kaidun is presented. The fragment is clas sified with EH3-4. This is the third type of enstatite chondrite that was found in this unique meteorite. The fragment is rich in metal nodu les, which can be subdivided into three textural types: (1) globular, (2) zoned, with massive cores and globular rims, and (3) having no int ernal structure. The sizes and compositions of kamacite globules in th e nodules and kamacite grains in the matrix are identical. The nodules contain small, commonly less than 5 mu m, inclusions of widely rangin g compositions: SiO2, albite glass, enstatite, roedderite, and a mixtu re of SiO2 and Na2S2. This is the first known occurrence of a simple a lkalimetal sulfide in nature. The inclusions may have formed by conden sation of material on the surface of metal grains. The nodules resulte d from the agglomeration of individual metal grains and the simultaneo us preservation, of condensates as inclusions. The processes of conden sation and agglomeration of the metal grams were synchronous. The incl usions may have formed by the disequilibrium condensation of gas of so lar composition or by equilibrium condensation of highly fractionated gas.