Impact Breccias

Sierra Madera Impact Breccia - 28g. 28 grams. Approximate size: 2.0" x 1.5" x 0.3". Location: Sierra Madera Crater, Pecos County, Texas. Thin slab of impact breccia in Permian limestone. Angular dark clasts sit in a light tan matrix, with smaller mixed fragments and faint pinkish banding along the edge. This is a sample of impact breccia in Permian limestone from the Sierra Madera Crater in Pecos County, Texas. Impact breccias are made of angular, shattered rock fragments held together by a fine-grained matrix or melted rock cement, created by the extreme shock and energy of a meteorite impact. The discovery of shatter cones, impact breccia, and shocked quartz in the 1960s helped provide unambiguous evidence that the Sierra Madera feature is an impact structure. It was created about 100 million years ago by the impact of an asteroid estimated to have been about 0.6 miles in diameter. The impact created an 8–10-mile-wide complex crater (astrobleme) featuring a 5-mile-wide central uplift and crater rim.