The most common constituent of sand, in inland continental settings and non-tropical coastal settings, is silica (silicon dioxide, or SiO2), usually in the form of quartz, which, because of its chemical inertness and considerable hardness, is resistant to weathering. The composition of sand varies according to local rock sources and conditions. The bright white sands found in tropical and subtropical coastal settings are ground-up limestone. Arkose is a sand or sandstone with considerable feldspar content which is derived from the weathering and erosion of a (usually nearby) granite. Some locations have sands that contain magnetite, chlorite, glauconite or gypsum. Sands rich in magnetite are dark to black in color, as are sands derived from volcanic basalts. The chlorite-glauconite bearing sands are typically green in color, as are sands derived from basalts (lavas) with a high olivine content. The gypsum sand dunes of the White Sands National Monument in New Mexico are famous for their bright, white color. Sand deposits in some areas contain garnets and other resistant minerals, including some small gemstones.
Black Rock Desert home of Burning Man is a playa, also known as alkali flat or sabkha, is a dry lakebed, generally the shore of, or remnant of, an endorheic lake. Such flats consist of fine-grained sediments infused with alkali salts. Their surface is generally very dry, hard and smooth in the summer months, but wet and very soft in the winter months. While the playa itself will be devoid of vegetation, they are commonly ringed by shadscale, saltbrush and other salt-tolerant plants that provide critical winter fodder for livestock and other herbivores
During the lake's peak around 12,700 years ago, the desert floor was under approximately 500 feet (150m) of water.