Polymict breccia
A polymict breccia is a rock made of broken fragments of several different rock types cemented together.
A polymict breccia is a breccia whose fragments come from more than one kind of rock. The prefix 'poly' means many. Breccias form when impacts shatter and mix surface material, and later compaction or heating binds the pieces together.
Howardites, the meteorites that give this website its name, are classic polymict breccias. They contain fragments of eucrite basalt and diogenite pyroxenite, along with impact melt and sometimes bits of carbonaceous chondrite, all from the surface of the asteroid Vesta. Many lunar meteorites are polymict breccias of highland and mare rocks, and some ureilites and chondrites are polymict too.
On a cut face, a polymict breccia often looks like a mosaic of light and dark angular pieces. Each fragment can be studied separately, so one stone may sample many places on its parent body. This makes polymict breccias especially valuable for learning about the variety of rocks on asteroids.
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