Buddingtonite

Buddingtonite is an ammonium feldspar 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 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
General
Category	Silicate mineral
Formula (repeating unit)	NH4AlSi3O8
Strunz classification	9.FA.30
Crystal system	Monoclinic
Crystal class	Prismatic (2) or sphenoidal (2/m)
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
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 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

• Erd RC, White DE, Fahey JJ, Lee DE (1964). "Buddingtonite, an ammonium feldspar with zeolitic water". American Mineralogist. 49 (7–8): 831–50.
• Felzer B, Hauff P, Goetz AFH (1994). "Quantitative reflectance spectroscopy of buddingtonite from the Cuprite mining district, Nevada". Journal of Geophysical Research. 99 (B2): 2887–95. Bibcode:1994JGR....99.2887F. doi:10.1029/93JB02975.
• Gulbrandsen RA (1974). "Buddingtonite, ammonium feldspar, in the Phosphoria Formation, southeastern Idaho". USGS Journal of Research. 2 (6): 693–7.
• Loughan FC, Roberts FI, Linder AW (1983). "Buddingtonite (NH₄-feldspar) in the Condor Oilshale Deposit, Queensland, Australia". Mineralogical Magazine. 47 (344): 327–34. Bibcode:1983MinM...47..327L. doi:10.1180/minmag.1983.047.344.07.
• Solomon GC, Rossman GR (1988). "NH₄<super>+</super> in pegmatitic feldspars from the southern Black Hills, South Dakota". American Mineralogist. 73: 818–21.
• Yang K, Browne PRL, Huntington JF, Walshe JL (2001). "Characterizing the hydrothermal alteration of the Broadlands-Ohaaki geothermal system, New Zealand, using short-wave infrared spectroscopy". Journal of Volcanology and Geothermal Research. 106 (1–2): 53–65. Bibcode:2001JVGR..106...53Y. doi:10.1016/S0377-0273(00)00264-X.
• Voncken JHL, van Roermund HLM, van der Eerden AMJ, Jansen JBH, Erd RC (1993) Holotype buddingtonite, an ammonium feldspar without zeolitic H₂O. American Mineralogist, 78, 204-209