12031 (7) - Pigeonite basalt
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Fact sheet
Description: 

This interesting rock is not well studied, nor characterized. 12031 is a coarse-grained (~2 mm), equigranular rock with a variable texture. Graphic intergrowths of pyroxene and plagioclase give way to a more granular, gabbroic texture. Elongated and externally skeletal ilmenite, tridymite laths and interstitial cristobalite constitute the rest of the rock. Magnesian olivine and Cr-spinel are absent and pyroxenes are neither lath-shaped nor porphyritic. Plagioclase occurs as large, anhedral, poikilitic grains with prominent and complicated twinning. Groundmass phases are remarkably coarse-grained. Troilite is associated with phosphate at the junction of pyroxene and pyroxferroite. At the junction, pyroxferroite breaks down to fayalite, cristobalite and Fe-rich pyroxene in wormy intergrowths.

The sample weighed 185 grams before analysis and is 3.23±0.07 billion years old (Rb-Sr).

Deterioration of the embedding resin has resulted in the growth of colourful crystallites around the thin section.

Further details of this and other Apollo samples are here: http://curator.jsc.nasa.gov/lunar/

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Not known
Ma = Millions of years ago
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igneous
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