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.

Scientists say that clastic sediments are well-sorted when the individual grains are all about the same size. When big chunks and tiny grains are mixed together, the sediments are considered poorly sorted. In general, the distribution of size of the particles in a clastic sedimentary rock may indicate how fast the water or wind transported the grains before they were deposited and ultimately became cemented into rock. The faster the flow, the larger the particles it can push. In some cases, unusually dense particles, such as nuggets of gold or magnetite, drop to the bottom of a stream or river sooner than similarly sized grains of lighter minerals. Also, after a lengthy period of movement through turbulent water, less resistant particles wear down or disintegrate altogether, leaving the more durable mineral grains behind. All these clues help geologists figure out the stories behind these fascinating rocks.