12040 (41) - Olivine basalt
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Fact sheet
Description: 

12040 is a slowly cooled olivine basalt with a high proportion of mafic minerals. This rock is roughly equigranular in texture, the largest crystals being 3-4mm in length and the average grain size 1 mm. 12040 contains evidence of accumulation of olivine. Hence the composition of 12040 does not represent that of a parent liquid. It has been described as a holocrystalline coarse-grained rock composed chiefly of pyroxene and olivine with minor plagioclase and opaque phases. Olivine occurs as clear equant anhedra or subhedra about 1 mm in size. Plagioclase occurs interstitially to olivine and pyroxene. Olivine may have formed late and/or re-equilibrated as the rock cooled. It occurs both as large inclusions in augite-pigeonite megacrysts and as separate grains associated with small pyroxene. The olivine and pyroxene in 12040 contain abundant melt inclusions.

The sample weighed 319 grams before analysis and is 3.3 billion years old (Rb-Sr).

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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