Gypsum dunes glow white because the sand grains are soft mineral
Most dunes are quartz, but some arid basins pile bright gypsum crystals into white dune fields when evaporite lakes dry and wind sorts the soft mineral.
Gypsum abrades easily and stays pale, so the dunes look like snowfields even under desert heat.
Color reveals chemistry. White dunes are salt-lake leftovers given wings — mineral beaches without an ocean.
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