Sand
Most sand is tiny bits of rock, often a hard mineral called quartz, worn down by water, wind, and ice. On some tropical beaches the grains are crushed shells and coral. Volcanic beaches can be black leftover lava.
On this page: where sand comes from, why beaches change color, how long sand takes to form, and how desert sand differs.
Read the answer below. In Giant, kids talk with characters and keep the adventure going.
Sand
Sand is a size, not one recipe. Grains are bigger than silt and smaller than pebbles. A lot of beach sand is quartz because quartz is tough. Softer minerals wear away first. Rivers, waves, glaciers, and wind do the grinding. In warm, clear water, animals build shells and reefs. Those break into pale sand. Fresh lava can smash into black glass-like grains. Every handful is a travel story.
0.06–2 mm
Sand grain size
Quartz
Common beach mineral
Shells
Many warm beaches
Lava
Black sand
Beach sand is different colors because the grains come from different rocks, shells, or lava, not because the water dyed them. Pale quartz and leftover feldspar look tan or white. Pink can come from garnet. Green olivine shows up on a few volcanic shores. Black sand is often basalt or volcanic glass. White Caribbean beaches are often crushed coral and shells. The parent material sets the color.
There is no single timer. A cliff can shed grains after one storm. A granite mountain can take thousands to millions of years to wear into a beach. Coral sand can build faster in a busy reef, then get tossed by a hurricane. Sand is also recycled. Waves sort it, bury it, and spit it out again. A grain you hold may be older than any castle you build with it.
Not always. Desert dunes are often piled by wind. The grains can be rounder because they bounce and chip in air. Beach sand is sorted by waves and may hold shells, salt, and wet clumps. Some deserts used to be seafloors. Some beach sand started inland and rode a river to the coast. Same word, different last ride.
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