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Madison County is a rich source of a pink-and-green granite called unakite
Jimmy Graves scans the edge of the Rose River in Madison County near Graves Mountain Lodge. Unakite can be found there, especially after a heavy rain washes it from the mountains a few miles away in Shenandoah National Park.
laura moyer/THE FREE LANCE-STAR
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Date published: 10/20/2008
SYRIA--Jimmy Graves crosses a concrete bridge over the Rose River and vanishes into a patch of fall-tinged shrubs.
He appears again minutes later, a stone in each hand.
The area has been pretty well picked over by rock hounds seeking chunks of Madison County's geologic pride, the dense granite called unakite.
But Graves can still spot some occasionally, and this fall day yields a few fist-size chunks and a cobble the size of a toy football.
Rinsed of caked mud and dried algae, the stones show their colors: green and pink, with silvery gray flecks.
Unakite--named after the Unaka range on the Tennessee-North Carolina line where it was first identified--is a visual treat. Its color combination makes it irresistible to collectors who carve and polish it into beads, paperweights and bookends.
Hunting for it along the Rose River is a popular pastime of the tourists who visit Jimmy Graves' family business, Graves Mountain Lodge, for a meal or a weekend.
On a sunny fall afternoon, it's easy to get caught up in the search without stopping to think about the origins of these pretty stones.
But the geologically curious might delve deeper--about 10 miles deep, according to College of William & Mary geology professor Christopher "Chuck" Bailey.
That's where the unakite story began 300 million to 400 million years ago, in a pressurized layer of hot rock deep in the Earth's crust.
As plates squeezed up to form the Appalachian Mountains, Bailey says, hot chemical-laden water percolated through a hard layer of feldspar buried under miles of younger rock.
The watery brew was about 550 to 750 degrees Fahrenheit--not hot enough to melt the rock, but hot enough to alter it.
Iron and calcium changed some of the feldspar into a different rock altogether, the green stone epidote. Potassium turned adjacent patches of feldspar pink. And grayish quartz filled in the gaps.
Over the next several hundred million years, the rock on the surface eroded and moved east toward the Atlantic Ocean, helping form what's now Virginia's Coastal Plain. As layers above it disappeared, the deep rocks that included patches of unakite became cooler and shallower.
At last they were left uncovered, and they jut throughout the Blue Ridge Mountains today.
Unakite can be found in spots all along the eastern Blue Ridge, Bailey says.