Diopside
| Diopside | |
|---|---|
Diopside - Bellecombe, Châtillon, Aosta Valley, Italy
|
|
| General | |
| Category | Silicate mineral |
|
Formula (repeating unit) |
MgCaSi2O6 |
| 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, grey |
| 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 | |
Diopside is a monoclinic pyroxene mineral with composition MgCaSi2O6. It forms complete solid solution series with hedenbergite (FeCaSi2O6) 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°.
Diopside is found in ultramafic (kimberlite and peridotite) igneous rocks, and diopside-rich augite is common in mafic rocks, such as olivine basalt and andesite. Diopside is also found in a variety of metamorphic rocks, such as in contact metamorphosed skarns developed from high silica dolomites. It is an important mineral in the Earth's mantle and is common in peridotite xenoliths erupted in kimberlite and alkali basalt.
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