France, July 18 -- In a valley in the Blue Ridge Mountains of North Carolina, some 800 metres above sea level, lie a few square kilometres that feed the global computer chip industry.

The Spruce Pine mining district is estimated to supply more than 80 percent of the world's ultra-pure quartz, a key material for making the semiconductors on which computers and other complex electronic devices depend. They are also essential for solar panels.

"We're seeing the development of the components industry, and with it the need for materials of extremely high purity," says geographer Laurent Carroue, director of research at the French Institute of Geopolitics (IFG) at Paris VIII University.

Spruce Pine produces some of the purest quartz in the w...