Allende meteorite minerals

The application of the laser probe to meteorite chronology is illustrated by a study of Ca-Al-rich inclusions from the Allende meteorite [7]. This study was able to show that the K in the inclusions studied mainly concentrated in veins and rims with very little, if any, K in the major minerals. The limit obtained is something of the order of 10 ppm. On the other hand, the major minerals do contain appreciable 40Ar. Individual chondrules and the matrix were also studied in the Allende meteorite from places adjacent to the Ca-Al-rich inclusions. For these samples the ages varied from 3.3 to 4.4 G.y. There appears to be evidence that the Allende meteorite has been subjected to numerous metamorphic events, presumably of a collisional origin. 

Pyroxenes from extraterrestrial sources provide unequivocal examples of Ti3+ —> Ti4+ IVCT and Fe2+ —> Ti4+ IVCT bands. For example, the iron-free green titanian pyroxene in the Allende meteorite discussed in 4.4.1 is the one irrefutable example of a mineral showing a Ti3+ — > Ti4+ IVCT transition. The position of the band at 666 nm (15,000 cm-1) shown earlier in fig. 4.2 is insensitive to pressure, but it does intensify at high pressures (Mao and Bell, 1974a), consistent with it representing a Ti3+ —> Ti4+IVCT transition between adjacent Ti3+ and Ti4+ ions located in edge-shared Ml octahedra in the pyroxene structure (fig. 5.13). 

Bums, R. G. and Huggins, F. E. (1973) Visible-region absorption spectra of a Ti3+ fassaite from the Allende meteorite A discussion. Amer. Mineral., 58, 955-61 [see Dowty and Clark (1973)]. 

Dowty E. and Clarke R. S., Jr. (1973) Crystal structure refinement and optical properties of a Ti fassaite from the Allende meteorite. Am. Mineral. 58, 230-242. 

CAFs - refractory inclusions, or Ca-Al-Inclusions, up to 2 cm across, enriched in Si-poor, Ca-Al-rich minerals. The most abundant source of CAIs is the Allende meteorite, which fell in 1969. 

Another fundamental difference is that while potassium is a minor element, and there are minerals that can be identified that contain relatively large amounts of potassium (e.g., orthoclase or biotite), iodine is a trace element, and is seldom a major part of a mineral. Hence it is usually not known what mineral contains the bulk of the iodine in an extraterrestrial sample. A notable exception is the mineral sodalite in the Allende meteorite, which contains the bulk of the iodine in that meteorite (Kirschbaum... 

Krot A. N., Petaev M. I., Zolensky M. E., Keil K., Scott E. R. D., and Nakamura K. (1998c) Secondary calcium-iron-rich minerals in the Bali-like and Allende-like oxidized CV3 chondrites and AUende dark inclusions. Meteorit. Planet. Sci. 33, 623-645. 

The overwhelming importance of type B CAIs during the first 20 years of CAI literature derives from several factors. First, and has been noted many times by many authors, these objects are large, abundant, and eye-catching within a very large meteorite (Allende) that fell in 1969 and was immediately distributed to scientists around the world. Second, their size and large crystals (commonly 0.5-1 mm for phases other than spinel) made them easy to study, especially for investigations that required mineral separates... 

The results of the chemical equilibrium calculations for the refractory lithophiles are also confirmed by the mineralogy and chemistry of the Ca, Al-rich inclusions in Allende and other meteorites. The major minerals in CAIs are the same ones predicted by the calculations, namely melilite (a solid solution of gehlenite CaALSiOr and akermanite Ca2MgSi2C>7), spinel, corundum, grossite, hibonite, and perovskite. Chemical analyses of CAIs show that the refractory lithophiles are enriched by an average of 20 times solar elemental... 

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