Lunar sample 65015.
This is an impact melt breccia, which is an impact breccia that was incompletely melted during impact heating. It consists of a matrix of crystallized liquid, now mostly pigeonite and plagioclase, enclosing a variety of monominerallic and polycrystalline fragments. This was collected by the Apollo 14 mission to the Fra Mauro crater, on the northeastern margin of Mare Nubium. The material represents part of the Mare Imbrium ejecta blanket. It has been dated at ~3.93 Ga.
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 |
40X, plane polarized light.
Compared to other breccias, this one is strikingly light-colored. This is because it contains no dark glass and rather little very fine-grained opaque material. The opaque material is coalesced into larger crystals, which in aggregate do not appear so dark. The breccia texture, however, remains. Some of the clasts, for example the larger one in the lower right, are annealed lithic fragments.
40X, cross polarized light.
In cross polarized light the patchy, poikilitic pigeonite can be seen enclosing fragments and new crystals of plagioclase and rare augite and olivine. The predominance of low-Ca pyroxene, abundance of plagioclase, and low olivine and opaque content indicates that this sample consists of reworked highland rocks.
100X, plane polarized light.
This closeup view shows some of the clasts in detail. The large plagioclase crystal to the upper right seems to have an overgrowth of plagioclase marked by a faint dark line paralleling the grain margin. A few other grains also have hints of overgrowths. Note that the opaques (mostly ilmenite) enclose other crystals.
100X, cross polarized light.
This shows in detail the poikilitic pigeonite crystals. The yellow grain toward the bottom is an augite crystal.
200X, plane polarized light.
Closeup view of the annealed feldspathic rock fragment seen in the first image. Notice how the enclosed pyroxene crystals are partly shaped by adjacent plagioclase.
200X, cross polarized light.
The annealed texture of this anorthositic fragment is obvious with abundant 120° grain boundary intersections. The mafic minerals are augite, possibly with some olivine.