Metaphorphic Rock Emerald Schist

Associated Smithsonian Expert: Leslie Hale, B.S.

Leslie Hale at the Monterey Bay Aquarium (California, USA) during a conference of museum collections managers

Photo by Smithsonian Institution, National Museum of Natural History, Department of Mineral Sciences

Leslie Hale, the Smithsonian’s rock and ore collections manager at the Smithsonian National Museum of Natural History, tells people that she is a “rock librarian.” While growing up in Bowie, Md., not far from the Smithsonian, Hale collected rocks and took a summer class on lapidary art (making jewelry out of stone). Her career choice was greatly influenced by her attendance at a magnet high school for science and mathematics and taking geology as a senior-year elective. Hale joined the Smithsonian staff shortly after finishing her bachelor’s degree at the University of Maryland in 1989. Today, she supervises two full-time staff members as well as several volunteers, interns, and contractors. She assists Smithsonian scientists and visiting researchers who want to use the museum’s extensive collection of rock and ore specimens. Hale also sends out rocks on loan to geologists at distant universities; she keeps track of the objects’ whereabouts and sends out requests for return or loan renewal. Finally, she gives tours of the Smithsonian’s geology research facilities, conducts inventories, answers questions from the public, and identifies rock specimens.

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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Deformed conglomerate rock, Death Valley, California, USA
Courtesy of Marli Bryant Miller

How Metamorphic Rocks Are Formed

High pressures and temperatures within the Earth's crust can change rocks from one type to another. Scientists call this process metamorphism, which comes from the Greek words for "after" and "form." At the junctions where the Earth's crustal plates collide, pushing up mountain ranges, or where one plate slides underneath another, the original rocks, or protoliths (from the Greek words meaning "first" and "rock") undergo reactions that change the chemical or crystal structure of the rocks with little or no actual melting. The grains of minerals within many metamorphic rocks are aligned in parallel due to the forces pushing on them. The pressure-temperature combination causes some sedimentary rocks to lose water molecules or become anhydrous.