Breccias are rocks that are made up of broken, angular fragments of other rocks, cemented together by finer grained material. Impact breccias form when a rock is struck by a meteorite. The "target" rocks are broken up and "glued" back together by melted rock once it solidifies. Impact breccias often contain multiple rock types because different layers of rocks are thrown out of the impact craters as "ejecta" and mix together.