Diopside
A calcium–magnesium pyroxene found in the oldest solids of the Solar System and in many chondrules.
Key facts
- Formula
- CaMgSi2O6
- Family
- Silicates
- Crystal system
- Monoclinic
What it is
Diopside is a high-calcium pyroxene, with calcium and magnesium in equal amounts. Iron can replace the magnesium, forming a series towards hedenbergite. In calcium-aluminium-rich inclusions (CAIs), diopside often carries aluminium and titanium; this variety was long called fassaite, a name no longer used for a separate mineral.
Where it is found
It forms rims and interiors of CAIs in carbonaceous chondrites such as Allende, where it grew from the hot gas or melt around the young Sun. It is also found in chondrules, in equilibrated ordinary chondrites, in aubrites and in nakhlites from Mars, where augite and diopside crystals grew in a thick lava flow.
How it is recognised
It is pale green to colourless, with two cleavages at nearly right angles and an inclined extinction angle under the microscope. Titanium-rich examples in CAIs are pale purple or brown.
Did you know?
Several new minerals, such as davisite and grossmanite, were discovered as titanium- or scandium-rich relatives of diopside in Allende CAIs.
Green chrome diopside is used as a gemstone.