Flint Run jasper

Flint Run jasper is the brown-to-yellow jasper of Warren County in northern Virginia, found along Flint Run between Front Royal and Luray. Streaks or pockets of red, green, blue and gray run through the brown and yellow, coloured by iron and other mineral inclusions. It formed where the Blue Ridge meets the carbonate rocks of the valley along overthrust faults: weathering of silica-rich volcanic rock freed iron oxide and silica, and groundwater laid the silica down in limestone. Artifacts cluster on the eastern side of the northern Shenandoah Valley near the South Fork of the Shenandoah River, and people used the stone from Paleoindian through Late Woodland times.

Jasper that precipitated from groundwater in carbonate rock at the contact between the Blue Ridge and the western carbonates along overthrust faults. Silica-rich volcanic rock supplied iron oxide and silica as it weathered, and fractures let groundwater carry the silica into the carbonates.