A clastic sedimentary rock that is made up almost exclusively of quartz sand (with or without chert), that is relatively free of or lacks a fine-grained matrix, a quartzite of sedimentary origin, or a “pure quartz sandstone”. The term generally signifies a sandstone with more than 90-95% quartz and detrital chert grains that are well-sorted, well-rounded, and cemented primarily with secondary silica (sometimes with carbonate) in optical and crystallographic continuity with the grains. The rock is characterized by stable but scarce heavy minerals (zircon, tourmaline, magnetite), by lack of body fossils, and by prominence of cross-beds and ripple marks. It commonly occurs as thin but extensive blanket deposits associated with widespread unconformities (e.g. an epicontinental transgressive deposit). Example: St. Peter Sandstone (Middle Ordovician) of midwestern U.S. The term was introduced by Tieje (1921, p.655) for a quartz sandstone whose interlocking particles were cemented by infiltration and pressure (in contrast to paraquartzite), and was used by Krynine (1948, p.149) in contrast to metaquartzite, but the term in this sense is objectionable because it is an exception to the use of “ortho-” for a metamorphic rock indicating an igneous origin and because “quartzite” is traditionally applied to quartzose rocks that break across instead of between grains. The term is essentially equivalent to quartzarenite and quartzitic sandstone.