Why quartz survives the journey to a beach
Quartz is made of silicon and oxygen, bonded in a compact structure. Those elements are common in Earth’s crust, and quartz is a major ingredient in many continental rocks. Feldspar is more abundant, but it is less resistant at Earth’s surface: water and weak acids can alter it into clay minerals, carrying some of its ingredients away in dissolved form.
Quartz is harder to change chemically. As rain, rivers, and waves break rock apart, its grains can be freed while less durable minerals are transformed or removed. The surviving grains may then be carried downstream and repeatedly reworked along the coast. Their persistence is chemical, not invincibility: waves can still chip, grind, and move them.
Why beaches have different colors and grains
A quartz-rich beach is one possible endpoint of this sorting, not a universal one. The rocks and sediments feeding a shoreline matter, as do the distance grains travel and the conditions they encounter. Where shells, coral fragments, dark volcanic minerals, or other local material dominate, the beach can look and feel quite different.
That makes beach sand a record of both geology and time: its grains reflect what nearby rocks supplied and which materials survived the trip.
