MINERALOGY AND PETROLOGY OF CHONDRITIC METEORITES

Chondritic meteorites are naturally divided into five chemical groups according to their chemical compositions. Within each group a range of textures exists which is generally interpreted as representing progressive degrees of recrystallization, although there are also significant primary variations in each group. In most chondrites the major minerals are olivine, orthopyroxene, albitic feldspar, troilite, calcic pyroxene, and metallic nickel-iron; the compositions of the silicate minerals are usually uniform within recrystallized chondrites and very similar for individual chondrites belonging to a given group. In unrecrystallized chondrites the minerals are usually quite variable in composition and the primary structures of individual chondrules are well preserved. Most of the properties of chondrites can be interpreted in terms of metamorphic equilibration and recrystallization of primary chondritic matter, although alternative hypotheses exist. © 1969.