Lunar 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.

 

Magnification key:

20x = 8 mm image width

40x = 4 mm image width

100x = 1.6 mm image width

200x = 0.8 mm image width

400x = 0.4 mm image width

500x = 0.32 mm image width


20X, plane polarized light.

 

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 intracumulus 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.



20X, cross polarized light.

 

Notice the variable birefringence of the pyroxenes. In part this is caused by composition variations in the pyroxene.



40X, plane polarized light.

 

Pyroxene and smaller olivine crystals with interstitial plagioclase and Fe-Ti oxides. Smaller, blocky opaque grains are chromite and ulvospinel that settled with the cumulates. Notice how the pyroxenes enclose many olivines and opaques.



40X, cross polarized light.

 

This more clearly shows the zoning in birefringence that reflects compositional zoning. In general, the large grain cores are augite rimmed by pigeonite. Notice the rounded olivine crystals enclosed by pyroxene.



40X, plane polarized light.

 

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.



40X, cross polarized light.

 

The freshness of this basalt is remarkable, compared to terrestrial basalts where weathering, oxidation, and hydrothermal alteration rapidly take their toll.



500X, reflected light.

 

This is a crystal of ulvospinel (pinkish region). From the ulvospinel have exsolved thin lamellae of ilmenite (brighter) and spinel (medium-gray). The adjacent olivine crystal  is dark gray.



500X, reflected light.

 

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.