U.S. Silica Holdings, Inc., together with its subsidiaries, engages in the mining, processing, and sale of commercial silica in the United States. It operates in two segments, Oil & Gas Proppants and Industrial & Specialty Products. The company offers whole grain commercial silica products to be used as fracturing sand in connection with oil and natural gas recovery, as well as in various size distributions, grain shapes, and chemical purity levels for manufacturing glass products. It also provides ground commercial silica products for use in plastics, rubber, polishes, cleansers, paints, glazes, textile fiberglass, and precision castings; and fine ground silica for use in premium paints, specialty coatings, sealants, silicone rubber, and epoxies. In addition, the company offers other industrial mineral products, such as aplite, a mineral used to produce container glass and insulation fiberglass; calcined kaolin clay, a mineral primarily used as a functional extender in paints, plastics, specialty coatings, and rubber; and adsorbent made from a mixture of silica and magnesium for preparative and analytical chromatography applications. It serves oil and gas recovery markets, as well as various industries, including, container glass, fiberglass, specialty glass, flat glass, building products, fillers and extenders, foundry products, chemicals, recreation products, and filtration products. As of February 26, 2013, U.S. Silica Holdings, Inc. controlled approximately 307 million tons of proven and probable recoverable mineral reserves. The company was formerly known as GGC USS Holdings, Inc. and changed its name to U.S. Silica Holdings, Inc. in July 2011. The company is headquartered in Frederick, Maryland. U.S. Silica Holdings, Inc. is a subsidiary of GGC USS Holdings, LLC.