Diopside

Diopside
Diopside – Bellecombe, Châtillon, Aosta Valley, Italy
General
Category	Inosilicate mineral
Formula (repeating unit)	MgCaSi2O6
IMA symbol	Di[1]
Strunz classification	9.DA.15
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	C2/c
Unit cell	a = 9.746 Å, b = 8.899 Å c = 5.251 Å; β = 105.79°; Z = 4
Identification
Color	Commonly light to dark green; may be blue, brown, colorless, white to snow white, grey, pale violet
Crystal 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 scale hardness	5.5–6.5
Luster	Vitreous to dull
Streak	white
Specific gravity	3.278
Optical properties	Biaxial (+)
Refractive index	nα= 1.663 – 1.699, nβ= 1.671 – 1.705, nγ= 1.693 – 1.728
Birefringence	δ = 0.030
2V angle	Measured: 58° to 63°
Dispersion	Weak to distinct, r>v
Melting point	1391 °C
References	[2][3][4]

Diopside is a monoclinic pyroxene mineral with composition MgCaSi
₂O
₆. It forms complete solid solution series with hedenbergite (FeCaSi
₂O
₆) 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,^[5] and a specific gravity of 3.25 to 3.55. It is transparent to translucent with indices of refraction of n_α=1.663–1.699, n_β=1.671–1.705, and n_γ=1.693–1.728. The optic angle is 58° to 63°.