Phosphates, Arsenates, and Vanadates
A large class of minerals includes compounds of metallic elements with the phosphate (PO43-), arsenate (AsO43-), and the vanadate (VO43-). radicals. Several members of this class, including apatite and monazite, are primary minerals, but most are secondary and are formed through alteration of metallic-ore minerals, such as sulfides of copper, iron, lead, and zinc. In general, most of these minerals are soft and brittle, and often occur in small inconspicuous masses or crystals. Many are brightly colored and yield very colorful specimens.
- Chesterman, Charles W. The Audubon Society Field Guide to North American Rocks and Minerals, Alfred A. Knopf: New York (1987), p. 471