buddingtonite

{{infobox mineral | name = Buddingtonite | image = | alt = | caption = | category = Tectosilicate minerals | group = Feldspar group | formula = NH4AlSi3O8 | IMAsymbol=Bud | IMAstatus = Approved (1964) | molweight = | strunz = 9.FA.30 | dana = 76.1.2.1 | system = Monoclinic | class = Prismatic (2) or sphenoidal (2/m) | symmetry = P21 (no. 4) or C2/m (no. 12) | unit cell = a = 8.57 Å, b = 13.03 Å, c = 7.18 Å; β = 112.73°; Z = 4 | color = Colorless | colour = | habit = Compact masses replacing plagioclase as pseudomorphs | twinning = | cleavage = Good on {001}, distinct on {010} | fracture = | tenacity = Brittle | mohs = 5.5 | luster = Vitreous | streak = Light grey to yellow (impure specimens) | diaphaneity = Transparent to translucent | gravity = 2.32 | density = | polish = | opticalprop = Biaxial (+) | refractive = nα = 1.530 nβ = 1.531 nγ = 1.534 | birefringence = δ = 0.004 | pleochroism = | 2V = Calculated: 60° | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = | impurities = | alteration = | other = | references = }}

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.