Geological processes have occasionally deposited sands composed of nearly 100% quartz grains. These deposits are identified and produced as sources of high-purity silica sand, which is essential for the glassmaking industry. Quartz sand is utilized in the production of container glass, flat plate glass, specialty glass, and fiberglass. High-purity quartz sandstone, known as quartz glass sand, is ideal for manufacturing high-quality glass. "Glass sand" refers to sandstone almost entirely made of quartz grains. Pictured is a specimen of the Oriskany Sandstone from Hancock, West Virginia. In some locations, the Oriskany is over 99% pure quartz. While much of it is used for container glass, some is selected for making lenses for the largest telescopes. The specimen measures about four inches (ten centimeters) across.
