Gypsum forms bladed concretions called desert roses or sand roses, growing in sediments that are subjected to concentrated brines. The crystals grow from a central point, and the roses emerge when the matrix weathers away. They don't last long at the surface, just a few years, unless someone collects them. Besides gypsum, barite, celestine and calcite also form roses. See other common mineral shapes in the Mineral Habits Gallery
Gypsum also occurs in a massive form called alabaster, a silky mass of thin crystals called satin spar, and in clear crystals called selenite. But most gypsum occurs in massive chalky beds of rock gypsum. It's mined for the manufacture of plaster, and household wallboard is filled with gypsum. Plaster of Paris is a roasted gypsum with most of its associated water driven off, so it readily combines with water to return to gypsum.