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A fine to medium-crystalline rock consisting of plagioclase and pyroxene.


Diabase is a mafic, holocrystalline, igneous rock equivalent to volcanic basalt or plutonic gabbro. Diabase is also called Dolerite. Diabase dykes and sills are typically shallow intrusive bodies and often exhibit fine grained to aphanitic chilled margins which may contain tachylite (dark mafic glass).


Diabase normally has a fine, but visible texture of euhedrallath shaped plagioclase crystals (62%) set in a finer matrix of clinopyroxene, typically augite (20-29%), with minor olivine (3% up to 12% in olivine diabase), magnetite (2%) and ilmenite (2%). Accessory and alteration minerals include hornblende, biotite, apatite, pyrrhotite, chalcopyrite, serpentine, chlorite, and calcite. The texture is termed diabasic and is typical of diabases.