In the loose sandstones of Oklahoma, barite forms "roses" like these. They're similar to gypsum roses, and sure enough, gypsum is also a sulfate mineral. Barite is much heavier, though; its specific gravity is around 4.5 (by comparison, that of quartz is 2.6) because barium is an element of high atomic weight. Otherwise, barite is hard to tell apart from other white minerals with tabular crystal habits. Barite also occurs in a botryoidal habit (as seen in the Gallery of Mineral Habits).
This specimen is massive barite from strongly metamorphosed dolomite marble in the Gavilan Range of California. Barium-bearing solutions entered the stone during this metamorphism, but conditions did not favor good crystals. The weight alone is the diagnostic feature of barite: its hardness is 3 to 3.5, it does not respond to acid, and it has right-angled (orthorhombic) crystals.
Barite is widely used in the drilling industry as a dense slurry—drilling mud—that supports the weight of the drill string. It also has medical uses as a filling for body cavities that is opaque to x-rays. The name means "heavy stone" and it's also known by miners as cawk or heavy spar.
