Sedimentary Rock Sandstone

Associated Smithsonian Expert: Catherine (Cari) Corrigan, Ph.D.

Cari Corrigan with two meteorites from the collection.

Photographed by Brittany M. Hance, Smithsonian Institution.

Dr. Cari Corrigan is a research geologist at the Smithsonian National Museum of Natural History who specializes in the study of rocks called meteorites that come from other planetary bodies in our solar system. While growing up in western Michigan, she often went hiking and exploring in the woods and lakes near her house. During her first two years in college, she took an astronomy class and a geology class, and wondered how she could combine the two. This led to her discovery of the field of planetary sciences, which she decided to try to to make her career. After earning her PhD from Case Western Reserve University studying Martian meteorites in 2004, she worked as a postdoctoral fellow at both the Smithsonian and at Johns Hopkins University Applied Physics Lab, and joined the Smithsonian permanently in 2008. In both 2001 and 2004, Corrigan participated in the Antarctic Search for Meteorites Program as a field member. These teams travel to Antarctica annually to collect meteorites from the Antarctic ice, where they have fallen and remained frozen since they fell to Earth. The program has returned over 20,000 meteorites for research and educational purposes since it began in 1976. At the Smithsonian, Corrigan curates this collection of Antarctic Meteorites, while also conducting research on both Antarctic and non-Antarctic meteorites from the Moon, Mars, and the asteroid belt.

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This image was obtained from the Smithsonian Institution. The image or its contents may be protected by international copyright laws.

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Overview of rock quarry in Kentland, IN, site of a large meteorite impact. Notice how layers on the left side of image are vertical, when they were originally deposited flat.
Photographed by Donald E. Hurlbert, Smithsonian Institution

About Kentland Quarry

Deep underneath the soil of Indiana lies some of the hardest rock around. Limestone was deposited as sediment at the bottom of an ancient ocean some 400 million years ago. Since then the ocean has disappeared, and the sediments turned into rock, and have been buried under hundreds of feet of more recent sediment. About 100 million years ago a large meteorite struck what is now northwest Indiana, creating an impact crater about 12 kilometers, or 7.25 miles, across - the fourth largest in the United States. The impact was large enough that the central area of the crater rebounded back upward. This created high ground that was not buried as deeply by the sediments that covered the rest of the crater and the Midwest.

Artist interpretation of a meteorite impact, creating an impact crater, shocked quartz, breccia, and shattercones.
Image created by Karen Carr Studio, Inc., used with permission

How People Build from Kentland Quarry

The large impact at Kentland caused two benefits that allow humans to use the limestone there today. First, the impact was large enough that there was a rebound effect, where the central area of the impact came back up several hundred feet. Since the rock is near the surface people can access it easily without needing to remove much soil above. Secondly, the impact fractured the rock making it much easier to remove from the ground. Today, limestone from the Kentland Quarry is used for concrete in bridges and buildings, asphalt, rail ballast, and laying the foundation for roads to local windmill farms.

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Artist interpretation of a meteorite impact, creating an impact crater, shocked quartz, breccia, and shattercones.
Image created by Karen Carr Studio, Inc., used with permission

About Shocked Quartz Sandstone

Sandstone is a sedimentary rock composed mostly of grains of the mineral quartz. At the Kentland Impact Structure the quartz grains are "shocked," meaning they were deformed by the energy released by a very large and sudden force. One can see that the rock is very "friable," or crumbly, which is a result of having been shocked, in this case by the impact of a large meteorite. Quartz responds to shock by fracturing and deforming along planes of weakness in the mineral's crystal structure. These features, called "planar deformation features," are only visible under a microscope.

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