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| Geol 2111: Igneous and Metamorphic Petrology Lunar rocks and meteorites The Earth's moon is characterized by two main provinces, the bright highlands and the dark, flat maria. The highlands are dominated a single rock type called anorthosite that is primarily made up of the mineral plagioclase feldspar. The maria regions are underlain by basalt, a dark-colored volcanic rock made up of the minerals plagioclase feldspar, olivine, and pyroxene. The moon is geologically old relative to the Earth as most of the rocks there formed between 4.55-3.20 Ga (Giga annum, or billions of years ago). In contrast, the oldest rocks on Earth are around 3.96 Ga, and our planet is still geologically active as new rocks are being formed today. Below are some photos of hand samples collected by the Apollo astronauts and photomicrographs of thin sections made from the different lunar rock types. These samples are used as part of an igneous petrology laboratory exercise in Geol 2111. All of the samples were on loan from NASA as part of the lunar educational sample program. Details about what is shown are notably lacking. If you have specific questions about what you see, feel free to email me.
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| Maria: broad, flat basins underlain by medium-grained mafic volcanic rocks; dominantly basalts with varying composition/chemistry (high-Mg, high-Ti); formed after massive early impacts and erupted at surface, filling giant impact crater basins; typically 3.9-3.2 Ga | |
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These lower photos are of an interesting unit called the "orange soil." It was originally thought to be part of the lunar regolith (soil), and Apollo 17 astronauts sampled it for study. It was discovered that the "soil" is actually made up of volcanic glass beads that have the same composition as mare basalt. Some of the beads have small crystals of the minerals olivine and ilmenite growing inside of them. The orange soil was likely formed by explosive volcanic eruptions (lava fountaining) at the lunar surface, and the melt crystallized very quickly in the lunar atmosphere into the spherical glass beads. The orange color comes from the high Ti content of the erupting lavas. |
Highlands: made up of medium- to coarse-grained mafic to ultramafic igneous rocks; dominated by anorthosite; formed early in the moon's evolution; typically >4.0 Ga |
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Site last updated:
Thursday, May 25, 2006 6:04 PM