Buddingtonite

Buddingtonite
General
Category Silicate mineral
Formula
(repeating unit)		 NH4AlSi3O8
Strunz classification 09.FA.30
Crystal symmetry Monoclinic 2 or 2/m sphenoidal
Unit cell a = 8.57 Å, b = 13.03 Å, c = 7.18 Å; β = 112.73°; Z = 4
Identification
Color Colorless
Crystal habit Compact masses replacing plagioclase as pseudomorphs
Crystal system Monoclinic
Cleavage Good on {001}, distinct on {010}
Tenacity Brittle
Luster Vitreous
Diaphaneity Transparent to translucent
Specific gravity 2.32
Optical properties Biaxial (+)
Refractive index nα = 1.530 nβ = 1.531 nγ = 1.534
Birefringence δ = 0.004
2V angle Calculated: 60°
References [1][2][3]

Buddingtonite is an ammonium feldspar with formula: NH4AlSi3O8 (note: some sources add 0.5H2O to the formula). It forms in hydrothermal areas by alteration of primary feldspar minerals. It is an indicator of possible gold and silver 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. It has also been reported from the sedimentary Phosphoria Formation in Idaho (Gulbrandsen, 1974), South Dakota (Solomon & Rossman, 1988), Wyoming, and Montana. It occurs in the oil shale deposit, near Proserpine, Queensland, Australia (Loughan, et al., 1983).

It was named for Arthur Francis Buddington (1890–1980), a petrologist at Princeton University.

References

  1. ↑ Handbook of Mineralogy
  2. ↑ Mindat.org
  3. ↑ Webmineral data