diopside

{{Infobox mineral | name = Diopside | category = Inosilicate minerals (single chain) | group = Pyroxene group, clinopyroxene subgroup | boxwidth = | boxbgcolor =#fff9b4 | image = Diopside Aoste.jpg | imagesize = 260px | caption = Diopside – Bellecombe, Châtillon, Aosta Valley, Italy | formula = MgCaSi2O6 | IMAsymbol = Di | molweight = | strunz = 9.DA.15 | system = Monoclinic | class = Prismatic (2/m) (same H-M symbol) | symmetry = C2/c | unit cell = a = 9.746 Å, b = 8.899 Å c = 5.251 Å; β = 105.79°; Z = 4 | color = Commonly light to dark green; may be blue, brown, colorless, white to snow white, grey, pale violet | habit = Short prismatic crystals common, may be granular, columnar, massive | twinning = Simple and multiple twins common on {100} and {001} | cleavage = Distinct/good on {110} | fracture = Irregular/uneven, conchoidal | tenacity = Brittle | mohs = 5.5–6.5 | luster = Vitreous to dull | polish = | refractive = nα= 1.663 – 1.699, nβ= 1.671 – 1.705, nγ= 1.693 – 1.728 | opticalprop = Biaxial (+) | birefringence = δ = 0.030 | dispersion = Weak to distinct, r>v | pleochroism = | 2V = Measured: 58° to 63° | fluorescence= | absorption = | streak = white | gravity = 3.278 | density = | melt = 1391 °C | fusibility = | diagnostic = | solubility = | diaphaneity = | other = | references = }}

Diopside is a monoclinic pyroxene mineral with composition . It forms complete solid solution series with hedenbergite () and augite, and partial solid solutions with orthopyroxene and pigeonite. It forms variably colored, but typically dull green crystals in the monoclinic prismatic class. It has two distinct prismatic cleavages at 87 and 93° typical of the pyroxene series. It has a Mohs hardness of six, a Vickers hardness of 7.7 GPa at a load of 0.98 N, and a specific gravity of 3.25 to 3.55. It is transparent to translucent with indices of refraction of nα=1.663–1.699, nβ=1.671–1.705, and nγ=1.693–1.728. The optic angle is 58° to 63°.