Digging for answers

George Washington University geology professor Richard Tollo and three of his undergraduate students are detectives of the Blue Ridge Mountains, looking for clues about rocks, their composition and how the Earth formed.

“The whole idea is to fully characterize very complicated rocks and to train students at the same time to become professional geologists,” says Mr. Tollo, who holds a doctorate in geology.

The geology students, hired by the U.S. Geologic Survey (USGS), are studying pyroxene-bearing rocks that are about 1 billion to 1.2 billion years old. The students observe and note the location of the rocks, the oldest in the metro area, making measurements and collecting samples for microscopic and geochemical analysis.

They are participating in the Educational Geologic Mapping Program, a research project under the Appalachian Blue Ridge Project that aims to provide background geological information for the region’s environmental and developmental issues.

“The mineralogy of rocks tells you a great deal about their origin,” says Mr. Tollo, who conducts most of his research in the Blue Ridge and the Culpeper Basin, a lowland area east of the Blue Ridge.

The Blue Ridge has two major types of rocks identified through mineralogy, the study of the properties and distribution of minerals, Mr. Tollo says.

Pyroxene-bearing rocks, including gneisses (banded with layers of dark and light minerals) and granites, were crystallized under high-pressure conditions from magma, a molten material below the Earth’s surface, he explains.

The rocks, which have other minerals, including quartz and feldspar, were lifted to the Earth’s surface when an ancient mountain belt, or range of mountains called Grenville, developed 1 billion years ago. At the time, a giant landmass, or supercontinent, called Rodinia formed with the mountain chain in the middle.

The second type of rock identified in the Blue Ridge is a bit younger, formed about 700 million to 730 million years ago, and can be found west of Gainesville and Warrenton. The rock is a granite with amphibole, a black-colored mineral, and fluorite, a mostly purple-colored trace mineral, among other minerals.

Pyroxene-bearing rocks are metamorphic, altered in material content and appearance by heat and pressure, says James Reger, principal geologist at the Maryland Geologic Survey in Baltimore.

Igneous rocks, such as granite, are formed from molten material from deep within the Earth that solidifies underground or on the surface, Mr. Reger says. Underground or intrusive rocks are dark in color and high in certain substances, such as iron and magnesium, and do not make it to the Earth’s surface, he says. Extrusives are lighter in color, often rich in silicon and aluminum, and do make it to the surface, he says.

Sedimentary rocks, such as shale and limestone, are loose weathered rock debris that can have organic material deposited by wind, water or glaciers, says Alex Speer, executive director of the Geologic Society of Washington, a nonprofit organization in Northwest focused on communicating research results.

“It really is a material world,” says Mr. Speer, who holds a doctorate in geology. “If there weren’t rocks and minerals, there isn’t much left.”

The forming of that world comes, in part, from platectonics. Platectonics occurs when continents collide and move apart, the movement driven by the heat flow within the Earth.

“Platectonics work at the rate fingernails grow … over tens to hundreds of millions of years,” says Diane Noserale, spokeswoman for USGS in Reston.

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