Impactites are formed when an asteroid or comet strikes the surface of the Earth and the impact forms a crater. The rocks of the area are blasted from the site and fall as debris. Some of the rock will be melted to one extent or another. Some melted to solid high quality glass some poorer fused into lump called Impactites and some of the rocks of the region may only be ribboned with glass. Much of the rock that is debris in the ejecta blank around the crater will be mixed material of different types.