The classification of chondritic meteorites. American Museum novitates ; no. 2085

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New York, N.Y. : American Museum of Natural History
"Prior's classification of the chondritic meteorites into enstatite, olivine-bronzite, and olivine-hypersthene chondrites is extended by the recognition of two more groups, the olivine-pigeonite and the carbonaceous chondrites. These groups are defined by chemical composition, most readily by the FeO/FeO+MgO mol per cent (in enstatite chondrites this is zero or near zero, olivine-bronzite chondrites 15-22, olivine-hypersthene chondrites 22-32, olivine-pigeonite chondrites 32-40, carbonaceous chondrites 40-50). However, the mineralogical composition is related to chemical composition, and the classification of an individual meteorite can be rapidly obtained by the presence or absence of olivine and its composition. The boundaries between different groups of chondrites are marked by hiatuses and discontinuities in chemistry and mineralogy, rather than continuous transitions. Meteorites belonging to different groups are notably unequal in abundance. Of more than 800 chondrites, nine are enstatite chondrites; 11, olivine-pigeonite chondrites; 14, carbonaceous chondrites; and the remainder, olivine-bronzite and olivine-hypersthene chondrites in approximately equal numbers. The chondrites as a whole show a uniformity of composition in terms of the non-volatile elements, except that the olivine-hypersthene chondrites contain about 5 per cent less iron than the other groups; they comprise Urey and Craig's low-iron type, whereas the other groups of chondrites belong to their high-iron type. The significance of these facts is discussed, and it is concluded that all chondritic meteorites were derived by processes of dehydration and reduction from a primary material similar in composition to the carbonaceous chondrites. The hiatuses and discontinuities between the different groups are ascribed to differences in the intensity of these processes and to a limited amount of chemical and phase differentiation"--P. 18.
20 p. : ill. ; 24 cm.
Includes bibliographical references (p. 18-20).