Sandstone, a type of sedimentary rock, looks like sand frozen in place. When quartz, feldspar, and other silica-containing minerals and rocks break into fragments between 0.1 and 2 mm (0.004 to 0.08 inches) across, scientists call the pieces sand. In deserts, on beaches, and under bodies of water, layers of sand grains build up over thousands or millions of years, until the accumulated pressure from the weight of those layers compact the sand grains into solid rock, a process called lithification. The sand grains are commonly cemented together by fine-grained quartz and calcite. Sandstone makes up 10 to 20 percent of all sedimentary rocks on Earth because its ingredients are among the most widespread minerals. They are found worldwide and form under a wide range of depositional environments and conditions. Detailed examination of the mineral grains and rock fragments in sandstones is necessary to help geologists interpret the source rock and the environment in which the sandstone was deposited. For example, coarser sand grains in the rock could indicate that blowing wind or running water removed the smallest, finest granules before lithification took place.

The sand grains in sedimentary rocks such as sandstone come from many different rocks and minerals and may have a variety of shapes and colors. Worldwide, the largest fractions of sand grains consist of quartz and feldspar, because these two silicates are among the most common minerals in Earth's crust. Quartz has the advantages of hardness and chemical stability; some quartz sand grains survive long enough to be recycled from old sandstones. Other silicate minerals, such as plagioclase and pyroxene, may also be found in sandstone. Geologists name varieties of sandstone based on their grain content: for example, arkose is a dark-colored, high-feldspar sandstone and the principal material in the Australian monolith known as Uluru, or Ayers Rock.