Feldspathic lunar meteorites
Pale breccias from the ancient lunar highlands, the most common kind of Moon rock to reach Earth.
- Classification
- Stony meteorites › Achondrites › Planetary achondrites › Lunar meteorites › Feldspathic lunar meteorites
- In our catalogue
- 96 meteorites
- Heaviest
- Shişr 162, 5.53 kg
Feldspathic lunar meteorites are breccias made mostly of anorthite, a calcium-rich plagioclase feldspar, broken and welded together by impacts. They come from the bright highlands that cover most of the Moon, including the far side never sampled by the Apollo astronauts.
Mineralogy and chemistry
Most of the rock is plagioclase feldspar close to pure anorthite, the calcium end of the series, with smaller amounts of low-calcium pyroxene and olivine. Clasts of anorthosite, norite and troctolite are cemented in a matrix of crushed minerals and glass, and some meteorites are impact-melt breccias that were partly melted and recrystallised. Iron content is low, typically about 3% to 5% iron oxide by weight, and thorium, a tracer of the KREEP component, is usually very low.
Two broad kinds are recognised. Regolith breccias formed from compacted lunar soil and carry glass spherules and solar-wind gases. Fragmental and impact-melt breccias formed deeper in impact debris.
Origin and formation
The anorthosite crust formed about 4.4 to 4.5 billion years ago, when plagioclase crystals floated to the top of the Moon's global magma ocean. Over the next few hundred million years, huge impacts broke, melted and mixed it. Feldspathic lunar meteorites come from all over the highlands. Because they are so low in iron and thorium, many must come from the far side or other regions far from the Procellarum KREEP Terrane, which the Apollo missions happened to sample.
They also test the magma ocean idea. Anorthosite clasts from different meteorites have somewhat different ages and compositions, suggesting the crust formed over a longer time, or in a more complicated way, than a single floating layer would imply. Some contain magnesium-rich rocks not sampled by Apollo.
Abundance and famous examples
They are the most common lunar meteorites. Allan Hills A81005, found in Antarctica and collected in January 1982, was the first meteorite recognised as coming from the Moon, its identification checked by comparison with Apollo samples. Yamato 791197, collected by Japanese teams in 1979, was soon afterwards recognised too. Dar al Gani 262 from Libya, Dhofar 280 from Oman, Kalahari 008 from Botswana and Northwest Africa 482, an impact-melt breccia, are other examples.
How to recognise one
Look for white to pale grey angular fragments in a darker grey or brownish glassy matrix, sometimes with tiny glass beads. The fusion crust is often thin, vesicular and greenish brown. With very little metal, these rocks attract a magnet only weakly. They can resemble terrestrial breccias, and only analysis can confirm a lunar origin.
Famous examples
- Allan Hills A81005 Lunar (anorth), Antarctica, 1981 · 31 g
- Dhofar 280 Lunar (anorth), Oman, 2001 · 251 g
- Northwest Africa 482 Lunar (anorth), 2000 · 1.02 kg
- Dar al Gani 262 Lunar (anorth), Libya, 1997 · 513 g
- Yamato 791197 Lunar (anorth), Antarctica, 1979 · 52 g
Related groups
- Lunar basalts and gabbros Dark volcanic rock from the lunar maria, the Moon's great lava plains.
- Mingled lunar breccias Breccias that mix highland and mare rock, from the borders between the two.
- Lunar meteorites Rocks from the Moon, found mainly in deserts and Antarctica.
- Eucrites Volcanic basalt from the crust of Vesta.
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