howardites

Howardites are a class of stony meteorites that belong to the HED (Howardite–Eucrite–Diogenite) grouping and are linked to asteroid 4 Vesta. They are understood to be regolith breccias formed by impact processes on Vesta’s crust, representing a mixture of surface materials rather than a single igneous rock type.

Petrologically, howardites are polymict breccias characterized by a mixture of eucrite and diogenite fragments embedded in a fine-grained, eucritic matrix. The clasts range from eucritic to diogenitic in nature, and the overall texture reflects fragmentation and reassembly on the asteroid’s surface. Mineralogy is generally dominated by pyroxene and plagioclase, with trace olivine and accessory minerals typical of HED meteorites.

Formation and significance: howardites are thought to form when impact events excavate and mix crustal materials on Vesta, followed by regolith gardening that re-cements fragments into a breccia. This texture preserves a record of crustal heterogeneity and impact processes, making howardites important for understanding the geology and early history of Vesta as well as the broader HED meteorite suite.

Occurrence and classification: howardites are one of the defining members of the HED meteorite group, alongside eucrites and diogenites. They are found in meteorite collections worldwide, with a substantial number recovered from Antarctic expeditions, and are used to study surface processes, crustal composition, and planetary differentiation on Vesta. See also eucrites, diogenites, and HED meteorites.