Mineralogy and Peterology of the Apollo 11 Lunar Sample

Details Mineralogy and Peterology of the Apollo 11 Lunar Sample Mineralogy and Peterology of the Apollo 11 Lunar Sample

Jan 1970

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1970saosr.307.....w&link_type=abstract

SAO Special Report #307 (1970)

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7

Scientific paper

We prepared and studied thin sections of 1676 rock fragments (diameter range 1 to 5 mm) from the Apollo 11 bulk sample. In almost all cases, the rocks are finegrained enough for fragments of this size to constitute representative samples. We found the following proportions of rock types, evidently a mixture from many sources: soil breccias, 52.4%; basalts, 37.4%; glasses, 5.1%; anorthositic rocks, 3.6%; others (including less than 0.1% recognizable meteoritic debris), 1.5%. The basalts range i in grain size from <1 μ to > 300 μ and consist largely of pyroxene (~ 50 wt.%; titaniferous augite or sub-calcic augite plus pigeonite; ~ 30 mole % ferrosilite end member), plagioclase feldspar (~25%, An90-100 in most cases), and ilmenite (~ 20%). Some basalt specimens are surprisingly rich in K2O (0.7%). Their specific gravity is about 3.3 gm/cm3. The glasses are impact-melted and range from deeply colored (brown, ornage-yelow) to colorless; from clear and uniform to swirly, vesicular, and heterogeneous. The soil breccia is a consolidated mixture of mineral, rock, and glass fragments in a fine-grained, dark matrix (mostly glassy, but also mineral particles). Cementation is probably due to partial shock vitrification of an initially loose surface soil. Overall composition of the breccias is essentially the same as that of the basalts. Only the 61 anorthosite fragments found were totally unexpected. These are light in color, low in density (~ 2.9 gm/cm3), and range from true anorthosites to anorthositic gabbros. They are much finer-grained (10 to 100μ) than terrestrial anorthosites, but apparently true cumulates. Their feldspar is slightly more calcic than basaltic feldspar; the mafic minerals are olivine (Fa30-50) and sub-calcic clinopyroxene. Ti content is low. The bulk composition of one such fragment, probably representative of most of them, matches the Surveyor VII analysis of ejecta from the highlands crater Tycho. We belive the anorthosites are derived from the highlands. A lunar structural model is proposed in which a 25-km anorthosite crust, produced by magmatic fractionation, floats on denser gabbro. Where early major impacts punched through the crust, basaltic lava welled up to equilibrium surface levels and solidified, forming the maria. An explanation for mascons is offered. Meteoritic debbris and shock effects on the lunar surface are also discussed. Zr content of the lunar material is ~ 400 ppm.

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