What is a breccia meteorite?
A breccia meteorite is made of broken fragments of rock cemented back together, usually by impacts on its parent body. Many meteorites, including howardites and most lunar meteorites, are breccias.
A breccia (pronounced brech-ee-a, from an Italian word for rubble) is a rock built from angular pieces of older rocks. On Earth, breccias form in landslides, fault zones and impact craters. In space, the main cause is collisions. Asteroids and moons have been struck again and again, shattering their surfaces and welding fragments together through the heat and pressure of later impacts. The broken pieces are called clasts, and the finer material holding them together is called the matrix.
Scientists describe breccias by what they contain. A monomict breccia contains fragments of just one rock type, broken but not mixed. A polymict breccia combines different rock types, sometimes from different parts of a body or even from different asteroids. A regolith breccia is made from the loose soil, or regolith, of a body's surface, and often contains gases implanted by the solar wind, proof that its grains once lay at the surface.
Some famous examples show the variety. Howardites, such as Kapoeta, which fell in what is now South Sudan in 1942, are polymict regolith breccias from Vesta. NWA 7034, nicknamed Black Beauty, is a Martian regolith breccia containing fragments with very old ages. Kaidun, which fell in Yemen in 1980, is one of the most bewildering breccias known, holding fragments of many different meteorite types in a single stone. The asteroid that produced the Almahata Sitta meteorites in Sudan in 2008 was a loose mixture of rock types, so its fragments vary dramatically.
On a cut and polished face, breccias look like a mosaic of lighter and darker pieces. They are valuable because a single stone can sample many rocks, recording a long history of collisions in one hand specimen.