Lunar thin section 60025
This highly brecciated lunar anorthosite was collected by the Apollo 16 mission to the lunar highlands southwest of Mare Tranquillitatis. It has been dated at 4.44 Ga, and so is one of the oldest lunar rocks analyzed.
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This rock is a highlands anorthosite, presumably a cumulate that formed as part of the early lunar crust. This rock is really a lithified anorthosite breccia or cataclastite. It contains ~98% plagioclase of An95 to An97. It apparently contains fragments from several different anorthosite bodies, rather than from a single, homogeneous body. Pyroxenes include augite and orthopyroxene, but olivine is rare. In cross-polarized light you can see a fractured and faulted plagioclase crystal (center) and numerous other deformed, faulted, and polygonized grains. Notice that all grain sizes exist, from large to very small. Field width is 8 mm.
Views in plane and cross-polarized light.
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Close-up of the central faulted grain. Small aligned pyroxene rods occur in this plagioclase, probably a primary igneous feature. Numerous small pyroxene grains are scattered about. Offset twin boundaries are clearly visible in cross-polarized light. Note the very small grain size of the matrix. Field width is 1.6 mm.
Views in plane and cross-polarized light.
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