diopside

Description

Diopside is a monoclinic pyroxene mineral with composition MgCaSi2O6. It is an important rock-forming mineral in several metamorphic and basic to ultrabasic igneous rocks, and is also found in meteorites. It forms complete solid-solution series with “hedenbergite” (FeCaSi2O6) and “augite” [(Ca,Na)(Mg,Fe,Al)(Si,Al)2O6] and partial solid solutions with “orthopyroxene” [(Mg,Ca)(Si,Al)2O6] and “pigeonite” [(Ca,Mg,- Fe)(Mg,Fe)Si2O6)]. The diopside–hedenbergite series is analogous to the amphibole series. Diopside has several varieties, including a chromium-rich gem variety called chrome diopside. Diopside 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 density of 3.25 to 3.55 g/cc. It is transparent to translucent with indices of refraction of η1 = 1.663–1.699, η2 = 1.671–1.705, and η3 = 1.693–1.728.

Physical properties

Habit: Prismatic, Blocky, Granular.
Color: white, yellowish green, black, or grayish blue.
Diaphaneity: transparent to translucent.
Luster: vitreous (i.e., glassy).
Streak: white green.
Cleavage: (110) good.
Twinning: {001}, {100}.
Fracture: brittle, conchoidal.
Occurrence: basic and ultrabasic igneous and metamorphic rocks.