Enstatite
A magnesium-rich pyroxene that dominates enstatite chondrites and aubrites.
Enstatite is the magnesium end-member of the orthopyroxene series, with the formula MgSiO₃. In most meteorites, pyroxene contains a fair amount of iron, but in enstatite chondrites and aubrites the enstatite is almost iron-free. These meteorites formed under highly reducing, oxygen-poor conditions, where iron stayed as metal or sulfide instead of entering silicates.
That reduced chemistry makes enstatite meteorites important for understanding where the Earth's building blocks came from. Their oxygen isotopes and several other isotope systems are close to Earth's, and some researchers argue that material like them made up a large share of the early Earth. Abee, an enstatite chondrite that fell in Alberta, Canada, in 1952, and the aubrite Norton County, which fell in the United States in 1948, are classic examples.
Almost iron-free enstatite is white or colourless, so aubrites look strikingly pale. In enstatite chondrites it sits among abundant metal and sulfides, giving a dark grey look. Under an electron beam, enstatite glows brightly in a technique called cathodoluminescence, which helps researchers map it in thin sections.
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