Quartz is the main component of ordinary beach sand and has the chemical formula SiO₂.
Quartz consists of silicon and oxygen arranged in a durable crystal structure. Its resistance to chemical weathering and abrasion allows quartz grains to survive transport by rivers, waves, wind, and glaciers.
Not all beach sand is mostly quartz. Some beaches are dominated by coral fragments, volcanic minerals, feldspar, shell material, or other local debris. Sand’s composition therefore records the geology of its source area and transport history.
Quartz is also important in granite and many sedimentary rocks. Its common varieties include amethyst, citrine, and smoky quartz, whose colors result from impurities or radiation-related defects.