Sand is a naturally occurring
granular material composed of finely divided
rock and
mineral particles.
The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-
tropical coastal settings is
silica (silicon dioxide, or SiO
2), usually in the form of
quartz.
The second most common form of sand is
calcium carbonate, for example
aragonite, which has mostly been created, over the past half billion years, by various forms of life, like
coral and
shellfish. It is, for example, the primary form of sand apparent in areas where reefs have dominated the ecosystem for millions of years like the
Caribbean.