In these rocks, much of the feldspar has transformed by shock into glass, known as maskelynite. Because of this contrasting surface expression, astronauts journeying back from the Moon could see this crater from well out in space. A SIR-B radar image of southern Ontario highlights two juxtaposed but unrelated craters that are very different in age, in size, and in structural state. The far larger Sudbury structure appears as a pronounced elliptical pattern, more strongly expressed by the low hills to the north. After Sudbury was initially excavated, magmas from deep in the crust invaded the breccia filling, to emplace against its walls.
Some investigators think that the resulting norite rocks are actually melted target rocks.
This igneous rock is host to vast deposits of nickel and copper, making this impact structure a multi-billion dollar source of ore minerals. Although about 23 m. y. old, much of the crater's morphology has survived erosion.