Impacts are rocks that are formed when a meteorite (impact) hits the Earth's surface. When a meteorite impacts, strong mechanical forces (high pressure) and high temperatures are generated that transform the Earth's rocks at the impact site. Among other things, existing rocks are crushed, new minerals are formed and the rocks are partially melted and cooled again in the form of impact glass. New minerals that are characteristic of impactites are varieties of quartz, such as stishovite and coesite, which are formed only under very high pressure.

The process that leads to the formation of impactites is called impact metamorphosis.