Gypsum sand dunes, White Sands National Park, New Mexico

Sea of snow?

At a quick glance, you might mistake these southern New Mexico dunes for massive snowdrifts. Although they do make for great sledding, the tiny crystals that form White Sands National Park are not ice but gypsum, a soft mineral often used in plaster and chalk. The pearly sands compose part of the largest gypsum field in the world, at 176,000 acres and more than 4 billion tons of sand. Extensive as it is, this sea of alabaster covers just a fraction of the Tularosa Basin, a vast desert valley that's larger than some US states at roughly 6,500 square miles.