U.S. Silica Holdings, Inc. produces and sells commercial silica in the United States. It operates through 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 sells its whole grain silica products 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; and building products, fillers and extenders, foundry products, chemicals, recreation products, and filtration products industries, as well as container glass, fiberglass, specialty glass, and flat glass products industries. As of December 31, 2014, the company had approximately 363 million tons of proven and probable recoverable mineral reserves. The company, formerly known as GGC USS Holdings, Inc., is headquartered in Frederick, Maryland.