Diabase

Diabase (pronunciation: /ˈdaɪ.əbeɪs/) or dolerite or microgabbro is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine grained to aphanitic chilled margins which may contain tachylite (dark mafic glass). Diabase is the preferred name in North America, dolerite is the preferred name in most of the rest of the world, where sometimes the name diabase is applied to altered dolerites and basalts, though many petrologists prefer the name microgabbro to avoid this confusion.