Lunar thin section 72275
This is sample of friable, porous, multiply-reworked feldspathic highland breccia from the Taurus-Littrow Valley area, in a range of mountains between Mare Serenetatis and Mare Tranquillitatis. It was collected by the Apollo 17 mission. The multiple episodes of reworking have caused this breccia to have within it fragments of earlier breccias.
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This low magnification view shows one large and several small basalt fragments. The basalts are referred to in Meyer (1987) as being “pigeonite basalts”, unrelated to the mare basalts and presumably older. There is also a dark breccia fragment to the lower left that itself contains smaller breccia fragments. The texture of the basalt fragments is more clear in cross-polarized light, even if pigeonite cannot be distinguished from augite. The mafic vs. plagioclase-rich fragments in the dark breccia fragment are clearly visible by their colors. Field width is 8 mm. Views in plane and cross-polarized light. |
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Close-up of one of the pigeonite basalt fragments, showing fractured pyroxenes with considerable dark, fine-grained material that is not all Fe-Ti oxides. In cross polarized light the pyroxenes clearly enclose many plagioclase crystals, and the pyroxenes are strongly zoned. Field width is 4 mm. Views in plane and cross-polarized light. |
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Close-up view of the breccia fragment seen above. The matrix is very dark, unlike the largely crystalline matrix surrounding this fragment. In cross-polarized light you can see numerous colorful mafic mineral fragments in the dark matrix, and two large feldspathic fragments. The fragment close to the center is mostly a single plagioclase crystal. The fragment at the top left is an annealed feldspathic breccia or melt breccia. The fragment on the left edge of the image is basalt. Field width is 4 mm. Views in plane and cross-polarized light. |
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Close-up of the annealed feldspathic breccia fragment. This actually contains considerable mafic material, ~40%, most of which has rather low birefringence. In cross-polarized light the partially annealed texture is more visible, with small scale development of triple junction grain boundaries. I interpret this to be a fine-grained norite breccia that has annealed to produce the smooth grain boundaries. Field width is 1.6 mm. Views in plane and cross-polarized light. |
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Rapidly quenched liquid fragment with glass and feathery and radiating plagioclase and pyroxene crystals. Field width is 0.8 mm. |
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Interstitial material between pyroxenes and lath-shaped plagioclase crystals in one of the pigeonite basalt fragments. Dark grays are silicates. Medium pinkish-gray is ilmenite. Creamy-brown is troilite. Bright white specks are native iron grains. This interstitial material may also contain alkali feldspar and silica. Field width is 0.8 mm. |
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Spongy iron grains possibly resulting from in situ reduction of silicate iron. Field width is 1.6 mm. |
