diallage, either of the two pyroxenes augite and diopside, which have well-developed, close-spaced, parallel partings commonly filled with magnetite or ilmenite. These filled partings are generally more pronounced than cleavage planes. Diallage is commonly dark green or bronze-coloured and often occurs as large crystals enclosing the silicate olivine in basic to ultrabasic rocks such as gabbro and peridotite. The term diallage is sometimes used in reference to a variety of diopside that has been altered by appreciable replacement by aluminum and other trivalent metal ions.