Olivine and pyroxene compositions in type II carbonaceous chondrites
Abstract
Random surveys were made of olivine and pyroxene compositions in ten C2 chondrites. Olivine distributions were found to peak sharply at 0.6-2 mole % fayalite, but grains containing up to 69 % fayalite are also present, as noted by Fredriksson and Keil (1964). Among the C2 chondrites studied, five parameters were noted to vary: content of chondrules, content of Fe-Ni metal, pyroxene: olivine ratio, percentage of olivine with high fayalite contents and modal fayalite content of the low-Fe 2+ olivine peaks. These variations correlate with one another, although imperfectly and it is suggested that they reflect stages through which primordial planetary or preplanetary material passed as it was more and more completely melted and reduced by early high-energy events. The dominant Fe 2+ content of C2 olivine and pyroxene would have been stable in an environment in which O:H - 1/50. To achieve this locally in the solar nebula, gas-dust fractionations by a factor of ~5000 must be postulated. Grosnaja, a C3 chondrite, was also surveyed and its mineral compositions are discussed from the viewpoint of possible metamorphic effects.
- Publication:
-
Geochimica et Cosmochimica Acta
- Pub Date:
- October 1967
- DOI:
- 10.1016/0016-7037(67)90144-5
- Bibcode:
- 1967GeCoA..31.2095W