Spruce Pine, North Carolina, USA
The geological history of the Spruce Pine Mining District is fascinating. About 380 million years ago, the African Continent was being forced toward the North American continent by plate tectonic forces. The focusing down of the Oceanic Crust underneath the North American continent produced tremendous friction generated heat from the two colliding continents. This friction generated heat, in excess of 2,000 degrees F, melted the surrounding rock 9 to 15 miles below the Earth's surface. This igneous molten rock was generated under intense pressure, which hydraulically pushed its way through the cracks of the host rock, and also melted contact areas of the host rock, sucking up rich mineral forming fluids.
It took an estimated 100 million years for this deeply buried (and insulated) mass to cool and crystallise. The slowly cooling mineral crystals grew within the Spruce Pine District to some of the largest feldspar and mica crystals in the world. After molton emplacement and cooling, it took many more millions of years of Appalachian Mountain building and subsequent erosion to expose the deposits we see today.