Associated Smithsonian Expert: Cara M. Santelli, Ph.D.

Dr. Cara Santelli visits a cave in eastern Tennessee (USA) to take samples of fungi that live in subterranean environments.

Photo by Sarah Carmichael, Appalachian State University

Dr. Cara Santelli is a research geologist and curator with the Department of Mineral Sciences at the Smithsonian National Museum of Natural History. Santelli grew up on the “Iron Range” of northeastern Minnesota, a region famous for its banded-iron formations. As a child, she loved digging in the dirt outdoors and bringing home pockets full of rocks, each of which was unique and beautiful. She always knew she wanted to be a scientist or engineer, but did not realize that her future lay in geology until she took a mineralogy course as an undergraduate at the University of Wisconsin. In 2007, Santelli earned a doctorate in marine geomicrobiology through a joint program of the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institute, and she joined the Smithsonian staff in 2010. She studies the impact of microbial activity on mineral formation, rock-weathering processes, and remediation of contaminated environments. One of the biggest thrills of her career was her dive 2.4 km (1.5 miles) underneath the Pacific Ocean in the deep-submergence vehicle Alvin. She still comes home from field excursions with pockets full of rocks.

Meet our associated expert

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

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Gypsum sand from White Sands National Monument, New Mexico, USA
Photograph by Mark A. Wilson, The College of Wooster

About Sand in Sedimentary Rocks

The sand grains in sedimentary rocks such as sandstone come from many different rocks and minerals and may have a variety of shapes and colors. Worldwide, the largest fractions of sand grains consist of quartz and feldspar, because these two silicates are among the most common minerals in Earth's crust. Quartz has the advantages of hardness and chemical stability; some quartz sand grains survive long enough to be recycled from old sandstones. Other silicate minerals, such as plagioclase and pyroxene, may also be found in sandstone. Geologists name varieties of sandstone based on their grain content: for example, arkose is a dark-colored, high-feldspar sandstone and the principal material in the Australian monolith known as Uluru, or Ayers Rock.