Buddingtonite is an ammonium with formula: NH4AlSi3O8 (note: some sources add 0.5H2O to the formula). It forms by hydrothermal alteration of primary feldspar minerals. It is an indicator of possible gold deposits , as they can become concentrated by hydrothermal processes. It crystallizes in the monoclinic crystal system and is colorless to white with a vitreous luster. Its structure is analogous to that of high sanidine (KAlSi3O8). Buddingtonite has a hardness of 5.5 and a specific gravity of 2.32.
Buddingtonite was discovered in 1964 at the Sulfur Bank mine near Clear Lake in Lake County, California (Erd et al., 1964). Clear Lake is at the north end of The Geysers geothermal area. It also occurs in the Tonopah, Nevada (Felzer et al., 1994) area and in hydrothermal areas in New Zealand (Yang et al., 2001) and Japan Phosphoria Formation in Idaho (Gulbrandsen, 1974), South Dakota, and Montana deposit, near Proserpine, Queensland (Loughan, et al., 1983).
It was named for Arthur Francis Buddington (1890–1980), a petrologist at Princeton University.