Silica sand is used in buildings and roads in the form of portland cement, concrete, and mortar, as well as sandstone. Most limestones have a granular texture. In many cases, the grains are microscopic fragments of fossil animal shells. Limestone has long fascinated earth scientists because of its rich fossil content. Much knowledge of the Earth's chronology and development has been derived from the study of fossils embedded in limestone and other carbonate rocks.
Limestone also has considerable commercial importance.
Limestones enriched in phosphate by the chemical action of ocean waters constitute a principal source of raw materials for the fertilizer industry. In well-developed crystals the mineral commonly has been called selenite. The fine-grained massive variety called alabaster is carved and polished for statuary and ornamental use when pure and translucent. Gypsite is the earthy pulverulent variety. It also occurs in considerable quantity in saline lakes and salt pans and is an important constituent of cap rock, an anhydrite-gypsum rock forming a covering on salt domes, as in Texas and Louisiana.