Discovery of shock-metamorphosed material establishes the impact origin of Lonar Crater. Coarse breccia with shatter coning and microbreccia with moderately shocked fragments containing maskelynite were found in drill holes through the crater floor. Trenches on the rim yield strongly shocked fragments in which plagioclase has melted and vesiculated, and bombs and spherules of homogeneous rock melt. As the only known terrestrial impact crater in basalt, Lonar Crater provides unique opportunities for comparison with lunar craters. In particular, microbreccias and glass spherules from Lonar Crater have close analogs among the Apollo specimens.

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Compositions and morphologies of dolomites, breunnerites, Ca-carbonates, Ca-sulfates and Mg, Ni, Na-sulfates, and their petrologic interrelations, in four CI chondrites are consistent with their having been formed by aqueous activity on the CI parent body. Radiochronometric data indicate that this activity took place very early in Solar-System history. No evidence for original ("primitive") condensates seems to be present. However, alteration apparently took place without change in bulk meteorite composition.

Iron, magnesium, and calcium in olivines and pyroxenes of 95 chondritic meteorites were analyzed with an electron microprobe. Of these, 86 were 'ordinary' chondrites, each having constant iron-magnesium ratios in olivine and pyroxene. Between different meteorites these ratios vary within three narrow ranges which reflect the It-and L-group chondrites, as well as a third group, designated the LL group. The ratio of iron in olivine to that in coexisting pyroxene is nearly constant (~1.1), particularly within the groups mentioned. A classification of stony meteorites based on the amount of iron in silicates and metal is proposed.It is shown that the iron content in the silicates is not related to the degree of metamorphism (recrystallization), and that therefore, the composition of the silicates was essentially established when the chondrules were formed. The ferrous iron also is not strictly related to the amount of metallic nickel-iron. Thus Prior's rule is not valid in its original sense, although it can be applied qualitatively when comparing the different groups of chondrites. The coexisting olivines and pyroxenes may not be in equilibrium in spite of their constant composition and the constant ratio between their iron contents. Furthermore, the metallic nickel-iron seems to have originated in the same melt as did the silicates. 3489 56 52 O8 04 OLIVINES AND RHOMBIC PYROXENES OF CHONDRITES