Apollo 12: Opaque oxides

Apollo 12: Opaque oxides Article

Haggerty, SE, Meyer, HOA. (1970). Apollo 12: Opaque oxides . EARTH AND PLANETARY SCIENCE LETTERS, 9(5), 379-387. 10.1016/0012-821X(70)90001-4

Electron microprobe analyses of eight optically isotropic chrome spinels (gray and blue) and seven optically anisotropic chrome ulvöspinels (tan, pink, khaki) have been carried out on four unshocked microgabbros from the Apollo 12 lunar samples. These analyses fall into two compositionally distinct groups along the join Fe2TiO4 (ulvöspinel)-FeCr2O4 (chromite) in the system (Fe,Mg)O-TiO2-(Cr,Al)2O3; compositionally the isotropic minerals range from Usp9Cr91 to Usp25Cr75, whereas the anisotropic phases range from Usp74Cr26 to Usp90Cr10 and hence lie outside the compositional limits of the Apollo 11 samples (Usp53Cr47). Up to 4 percent by weight of Fe2O3 is inferred to be present in the spinels. A khaki spinel containing 90 percent of the ulvöspinel molecule is the richest Fe2TiO4 phase yet found in nature. Chrome ulvöspinels are considered to be a new series of nonisometric phases along the join Fe2TiO4-FeCr2O4. Based on coexisting Usp90 and Ilm100, estimates for the temperature and f{hook}O2 of crystallization do not provide a unique solution, but at 1200°C the f{hook}O2 is 10-11.5. © 1970.