The borates are compounds of one or more metallic elements with the borate (BO33−) radical. There are two types of borates: the first, primary type is anhydrous (without water), and develops in igneous and metamorphic environments, where it is both rare and stable; the second type, the hydrous borates, develop in sedimentary rocks at the bottom of playas in arid regions. Many of the hydrous borates are readily soluble in water, and the dryness of their environment aids greatly in their preservation. The hydrous borates are brittle and relatively soft, and are white, colorless, or transparent. The anhydrous borates are dark in color and heavy.
- Chesterman, Charles W. The Audubon Society Field Guide to North American Rocks and Minerals, Alfred A. Knopf: New York (1987), p 447'