oligoclase

{{Infobox mineral | name = Oligoclase | category = Tectosilicate minerals | group = Feldspar group | series = Plagioclase feldspar series | boxbgcolor = | image = Oligoclase-4jg47a.jpg | imagesize = 260px | caption = Oligoclase from Chihuahua, Mexico | formula = (Ca,Na)(Al,Si)4O8 (Na:Ca = 70:30 to 90:10) | IMAstatus = Variety of albite | molweight = | system = Triclinic | class = Pinacoidal () | symmetry = P (no. 2) | color = Usually white, with shades of grey, green, or red | habit = | twinning = | cleavage = Perfect {001}, Good {010}, Poor {110}. | fracture = Uneven, sub-conchoidal | tenacity = | mohs = 6 to 6.5 | luster = Vitreous | polish = | refractive = nα = 1.533–1.543; nβ = 1.537–1.548; nγ = 1.542–1.552 | opticalprop = | birefringence = 1st order | dispersion = | pleochroism = | fluorescence= | absorption = | streak = White | gravity = 2.64 to 2.66 | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = | other = | references = }}

Oligoclase is a rock-forming mineral belonging to the plagioclase feldspars. In chemical composition and in its crystallographic and physical characters it is intermediate between albite (NaAlSi3O8) and anorthite (CaAl2Si2O8). The albite:anorthite molar ratio of oligoclase ranges from 90:10 to 70:30.