15597 (18) Vitrophyric Pigeonite Basalt
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Fact sheet
Description: 

15597 is a pyroxene vitrophyre consisting mainly of acicular pyroxene phenocrysts, typically with a glass core, set in a matrix of brown glass which shows incipient crystallisation in only a few places. The texture is locally variolitic but sometimes radiate - the latter being the result of rapid cooling (see rotation 1). The pyroxene crystals are composed of a pigeonite centre epitaxially rimmed by augite. Scattered Cr-spinel and metasilic iron globules also occur. Vesicles range in size from a few tens to ~500 microns. 15597 is thought to be an important lunar sample, because it was quenched from high temperature giving important insight to the crystallisation history and cooling rate of lunar basalts.

The sample weighed 147.5 grams before analysis. It has not been dated.

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

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Ma = Millions of years ago
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igneous
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