One type of meteorite in the HED (Howardite, Eucrite, Diogenite) achondrite group. Howardites are named after the English chemist Edward Howard (1774-1816), one of the pioneers of meteoritics. Consisting mostly of eucritic and diogenitic clasts and fragments, howardites are polymict breccias. However, they can also contain dark clasts of carbonaceous chondritic matter, other xenolithic inclusions, and impact melt clasts, indicating a regolith origin.

Howardites are defined by their ratio of eucritic and diogenitic material.  Howardites must contain 10% or more eucritic material and 10% or more diogenitic material – the mix can be 10% eucritic and 90% diogenitic material, or 90% eucritic and 10% diogenitic material.

Howardites likely represent regolith breccia from the surface of the asteroid 4 Vesta, consisting of eucritic and diogenitic debris excavated by the large impact that created the enormous crater near 4 Vesta’s south pole. These fragments mixed with parts of the chondritic impactor, and the mixture was subsequently pulverized and metamorphosed by smaller impacts and the solar wind to form a regolith. Similar regoliths cover the surface of the Moon and as is the case with howardites, lunar regolith breccias display high abundances of noble gases that have been implanted into the rock by the solar wind.

Some or all content above used with permission from J. H. Wittke.

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