Sandstone, a porous sedimentary rock composed of grains of sand usually held together by a natural cement, such as lime. Various minerals in sandstone, such as feldspar, garnet, or magnetite, may color it yellow, brown, red, or gray. Sandstone is sometimes marked with animal tracks and may contain fossilized plants and animals.
Depending on the degree of cementation, sandstone may be hard and durable or fragile and easily crumbled. Durable forms, such as brownstone, are frequently used as a building material. In underground formations, sandstone often acts as a natural reservoir for water, oil, or natural gas.