Sand behaving at times like a solid, at times a liquid and at times a gas, it is a master shape-shifter. Formed by wind and water, sand allows large-scale geography to play out in miniature: settling into ripples, channels, canyons, valleys and deltas.
Sand is born as tiny pieces break away from rock. Young grains have rough edges, which smooth with time. The roundest grains are found in the desert, where the constant shifting winds rub the grains against each other, grinding them to a smooth polish. Because of this, dunes, like those of the Sahara, move in vast waves.
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