| Abstract: | A single crystal of untwinned orthopyroxene from lunar anorthosite sample 15415, with composition (Mg1.14Fe0.80Mn0.02Ca0.04)(Si1.97Al0.03)O6, has a unit cell in space group Pbca with a = 18.310(15) A ??, b = 8.904(10) A ??, c = 5.214(7) A ??, containing 2 formula units. A set of 742 counter-measured intensity data made with MoK?? radiation has been used to refine the crystal structure in isotropic thermal mode to R = 0.116. Anisotropic refinement led to R = 0.092, but thermal parameters are distorted by non-random errors resulting from poor crystal texture. The resulting structure is in close agreement with that obtained by Ghose [9] for a hypersthene from Greenland. A parameter q, which gives (MgqFe1-q) for cation site M(1) and (Mg1.14-qFeq-0.18Ca0.04) for site M(2), was included in the least-squares analysis, yielding q = 0.90(1). This orthopyroxene has the high degree of cation order expected of pyroxenes subjected to Apollonian metamorphism at lower than 500-600??C. No evidence exists for a subsequent thermal event of sufficient intensity to disorder the pyroxene. On the basis of previous laboratory studies of argon-release patterns of lunar plagioclase and order-disorder kinetics of terrestrial pyroxenes, we attribute the reported isotopic age (3.9-4.1 AE) to cessation of metamorphism, perhaps caused by impact excavation. ?? 1978. |
| Genre: | Article |
| ProdID: | 70010379 |
| Citation Author: | Evans, Jr. , H. T.; Stephen, Huebner, J.; Konnert, J. A. |
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| Citation End Page: | 484 |
| Citation Issue: | 3 |
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| Citation Language: | English |
| Citation Larger Work Title: | Earth and Planetary Science Letters |
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| Citation Number Of Pages: | 9 |
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| Citation Search Results Text: | The crystal structure and thermal history of orthopyroxene from lunar anorthosite 15415; 1978; Article; Journal; Earth and Planetary Science Letters; Evans, Jr. , H. T.; Stephen, Huebner, J.; Konnert, J. A. |
| Citation Start Page: | 476 |
| Citation Volume: | 37 |
| Citation Year: | 1978 |
| Type: | citation/reference |
| Text: | The crystal structure and thermal history of orthopyroxene from lunar anorthosite 15415; 1978; Article; Journal; Earth and Planetary Science Letters; Evans, Jr. , H. T.; Stephen, Huebner, J.; Konnert, J. A. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| Date Other: | Sun, 1 Jan 1978 00:00 -0600 |
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