Petrographic investigation and high-voltage electron microscopy of an anorthosite fragment from Luna 20 landing site

Details Petrographic investigation and high-voltage electron microscopy of an anorthosite fragment from Luna 20 landing site Petrographic investigation and high-voltage electron microscopy of an anorthosite fragment from Luna 20 landing site

Apr 1977

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1977e%26psl..34..403b&link_type=abstract

Earth and Planetary Science Letters, vol. 34, no. 3, Apr. 1977, p. 403-410.

Computer Science

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Anorthosite, Electron Microscopes, High Voltages, Lunar Landing Sites, Lunar Rocks, Petrography, Chemical Composition, Crystal Dislocations, Feldspars, Fragments, Grain Boundaries, High Energy Electrons, Pyroxenes, Spinel

Scientific paper

A 2-mm fragment of an anorthosite was investigated in transmitted light and by high-voltage electron microscopy. A modal composition of 76% plagioclase (anorthite), 23% pyroxene (pigeonite), and about 1% spinel (pleonaste) was deduced. The results indicate a slight olivine-normative chemical composition. The rock is hypidiomorphic to idiomorphic fine-grained with a well-defined parallel-oriented fabric. Under the petrographic microscope, the plagioclase crystals show twinning only along (010) composition planes (predominantly Carlsbad twins). The dislocation density is low and the dominating defect structures are small-angle grain boundaries. Features indicative of shock were not observed. It is concluded that the rock fragment is in its original state, and that crystallization most likely occurred under plutonic conditions in a deep crustal region with the dominant assemblage: plagioclase + pyroxene + spinel.

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