The chemical composition of sand is primarily SiO2, or silica. Silica, which is also named as quartz, is a type of mineral that makes up most of the sand types like beach sand.
Quartz, which does not break easily, can be found in various types of rocks. Granite, which is a plutonic rock, and sandstone, which is a sediment rock, both have a high quartz content. Chemical and mechanical weathering results in sand. Whether a sand grain is rounded and smooth or angular depends on how it traveled downstream.
In the United States, sand grains are divided into five types according to their size: very fine, fine, medium, coarse and very coarse.