The sulfates are compounds of one or more metallic elements with the sulfate ion. This is a large class of minerals, whose members have few properties in common. In general they are light in color and transparent to translucent. None are hard, and most are fragile.
- Chesterman, Charles W. The Audubon Society Field Guide to North American Rocks and Minerals, Alfred A. Knopf: New York (1987), p. 453