Lunar thin section, sample 12005
This rock is an olivine-rich cumulate that is thought to have formed in the lower parts of a mare basalt lava lake. The sample was collected from the southeastern end of Mare Procellarum by the Apollo 12 mission.
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This sample is interpreted to be a lava lake cumulate. It is very rich in olivine and pyroxene. Most of the larger oxides and plagioclase are interstitial, having grown in the intra-cumulus pore spaces. The two largest grains occupying the center are olivine crystals, with tiny, oriented arrays of trapped melt inclusions. White is plagioclase, brown is pyroxene. In the cross-polarized light image, notice the variable birefringence of the pyroxenes. This is partly caused by composition variations. Field width is 8 mm. Plane and cross-polarized light views. |
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Pyroxene and smaller olivine crystals with interstitial plagioclase and Fe-Ti oxides. Smaller, blocky, opaque grains are chromite and ulvöspinel that settled with the cumulates. Notice how the pyroxenes enclose many olivines and opaques. In cross-polarized light you can more clearly see the zoning in birefringence that reflects compositional variation. In general, the large grain cores are augite rimmed by pigeonite. Notice the rounded olivine crystals enclosed by pyroxene. Field width is 4 mm. Plane and cross-polarized light views. |
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Euhedral and subhedral olivine grains enclosed in pyroxene and interstitial plagioclase. Notice how plagioclase encloses numerous euhedral and subhedral olivine crystals, and both plagioclase and pyroxene enclose abundant small euhedral chromite. crystals. The freshness of this basalt is remarkable, compared to terrestrial basalts where weathering, oxidation, and hydrothermal alteration rapidly take their toll. Field width is 4 mm. Plane and cross-polarized light views. |
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This is a crystal of ulvöspinel (pinkish region). From the ulvöspinel have exsolved thin lamellae of ilmenite (brighter) and spinel (medium-gray). The adjacent olivine crystal is dark-gray. Field width is 0.32 mm. |
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Trapped interstitial melt that quenched to a fine network of skeletal olivine and pyroxene (medium gray) and ilmenite (white). Darker gray regions are plagioclase and possibly other silica-rich minerals, and residual glass. Field width is 0.32 mm. |
