sandstone

Sandstone refers to a sedimentary rock with grains between 1/16 millimeter and 2 mm in size (siltstone is made of finer grains). Therefore sandstone doesn't signify any particular mineral, but in practice, sandstone is usually almost all quartz. Most sandstones, however, have small amounts of other minerals—clays, hematite, ilmenite, feldspar, and mica—that add color and character to the quartz matrix. Sandstones with greater amounts of impurities are classified as wacke or graywacke. Sandstone forms wherever sand is laid down and buried. Usually this is offshore from river deltas, but desert dunes and beaches can leave sandstone beds in the geologic record too. Sandstone does not usually contain good fossils because the energetic environments where sand beds form don't favor their preservation. As a landscaping and building stone, sandstone is full of character, with warm colors, and can be quite durable. China is now the world's largest exporter of sandstone.