Clinopyroxene
Clinopyroxene is the group of pyroxene minerals with a monoclinic crystal structure, including augite and pigeonite.
Clinopyroxene is the other major branch of the pyroxenes. Its crystal building block is monoclinic, slightly tilted on one axis, and that tilt allows it to hold more calcium than orthopyroxene. Common clinopyroxenes include augite, which is calcium-rich, diopside and the low-calcium pigeonite.
These minerals crystallise from basaltic magmas, so they are found in eucrites, shergottites, nakhlites, angrites and lunar basalts. Nakhlites from Mars are made mostly of augite crystals that piled up in a lava flow or shallow intrusion. In chondrites, small amounts of clinopyroxene appear in chondrules and grow during heating as the rock equilibrates.
Under crossed polars clinopyroxene typically shows inclined extinction, meaning it goes dark at an angle to its cleavage. Its composition records the temperature at which it formed, so pairs of coexisting pyroxenes act as a natural thermometer for the history of a meteorite.
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