This Special Section appeared in May 2015 Rock Products and features comprehensive resources on Frac Sand geology, production, news, equipment and technology. Frac sand is a specialized sand that is added to fracking fluids that are injected into unconventional oil and gas wells during hydraulic fracturing. While the principal source for frac sand is the traditional glass sands of the Midwest that are primarily pure silica, the high silica content is but one of the necessary criteria. Among the additional specifications are requirements for high sphericity/roundness, a uniformly medium- to coarse-grain size, high crush resistance, low solubility, low turbidity, and good friability. Additional factors that influence the economics of frac sand mining are the deposit’s accessibility at or near the surface, areal extent and thickness, textural uniformity, nearness to trucking and rail transportation routes, and proximity to the active unconventional petroleum basins.