EH chondrite
An EH chondrite is an enstatite chondrite with high total iron and small chondrules, formed in very oxygen-poor conditions.
EH chondrites are one of the two main groups of enstatite chondrites. The H stands for high iron: they contain more total iron, and more metal, than their EL cousins. Their chondrules are small, often under half a millimetre, and their main mineral is nearly iron-free enstatite pyroxene.
They formed in extremely reducing conditions, with so little oxygen that silicon dissolved into their metal and normally oxygen-loving elements formed sulfides such as niningerite and oldhamite. Abee, which fell in Alberta, Canada, in 1952, is a famous EH4 impact-melt breccia, and Indarch, which fell in Azerbaijan in 1891, is an EH4 chondrite.
Enstatite chondrites have oxygen isotopes almost identical to Earth's and the Moon's, and similar isotopes of several other elements. That has led some researchers to suggest that much of Earth was built from material resembling them, although their chemistry does not match Earth's exactly. Their sulfides react with moisture, so they need dry storage.
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