pigeonite

{{Infobox mineral | name = Pigeonite | category = Inosilicate minerals (single chain) | group = Pyroxene group, clinopyroxene subgroup | boxwidth = | boxbgcolor =#C27933 | image = PyroxeneExsol_0.5mmm.jpg | imagesize = | alt = | caption = Polarized light microscope image of part of a grain of orthopyroxene containing exsolution lamellae of augite The texture documents a multistage history: (1) crystallization of twinned pigeonite, followed by exsolution of augite; (2) breakdown of pigeonite to orthopyroxene plus augite; (3) exsolution of augite parallel to the former twin plane of pigeonite. (long dimension 0.5 mm, Bushveld igneous complex) | formula = | IMAsymbol = Pgt | molweight = | strunz = 9.DA.10 | dana = 65.01.01.04 | system = Monoclinic | class = Prismatic (2/m) (same H-M symbol) | symmetry = P21/c | unit cell = a = 9.7, b = 8.95, c = 5.24 [Å]; β = 108.59°; Z = 4 | color = Brown, greenish brown-black | colour = | habit = Prismatic crystals, to 1 cm; granular, massive. | twinning = Commonly twinned simply or multiply on {100} or {001} | cleavage = Good on {110}, (110) ^ (10) ~87° | fracture = Conchoidal | tenacity = Brittle | mohs = 6 | luster = Vitreous to dull | streak = Grey white | diaphaneity = Semitransparent | gravity = 3.17 – 3.46 measured | density = | polish = | opticalprop = Biaxial (+) | refractive = nα = 1.683 – 1.722 nβ = 1.684 - 1.722 nγ = 1.704 – 1.752 | birefringence = δ = 0.021 – 0.030 | pleochroism = Weak to moderate; X = colorless, pale green, brown; Y = pale brown, pale brownish green, brownish pink; Z = colorless, pale green, pale yellow | 2V = 0 – 30° measured | dispersion = weak to distinct | extinction = | length fast/slow = | fluorescence= | absorption = | melt = | fusibility = | diagnostic = | solubility = | other = | alteration = | references = }}

Pigeonite is a mineral in the clinopyroxene subgroup of the pyroxene group. It has a general formula of . The calcium cation fraction can vary from 5% to 25%, with iron and magnesium making up the rest of the cations.