File:Montoume Breccia (214 Ma, Late Triassic; Rochechouart Impact Structure, Haute-Vienne, France) 1.jpg

English: Montoume Breccia (suevite) (field of view 8.1 centimeters across)

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France’s deeply eroded Rochechouart Impact Crater is a fascinating place, both for its rocks and the significance of its impact date. Rochechouart is located in Haute-Vienne Department of west-central France. Impact breccias have long been used in the area as building stone - spectacular examples can be seen in the Rochechouart Castle. The rock shown here is one of many specific lithologies found in the Rochechouart Crater area. It's a reddish suevite. “Suevite” is a term used by impact geologists to refer to polymict impact breccias that include glassy and/or frothy melt clasts derived from impact melting. This particular reddish suevite is informally called the “Montoume Breccia”. It contains angular clasts of granite, gneiss, schist, and glassy/frothy melt of varying sizes, all set in a clastic matrix.

What particularly intriguing about the Rochechouart Crater is not its surficial appearance (it's so deeply eroded that the diameter can only be broadly estimated at 20-30 km), but its age. The Rochechouart impact event has been dated to 214 million years, during the Norian Stage of the mid-Late Triassic. Several other impact craters on Earth have been dated to or very close to 214 million years as well (for example, Quebec's very large Manicouagan Crater). It's been suggested that the end-Triassic mass extinction may have been caused by a chain-of-impacts event similar to the 1994 impact of Comet Shoemaker-Levy 9 with Jupiter.