Diabase

Diabase (/ˈdaɪ.əˌbeɪs/), also called dolerite (/ˈdɒl.əˌraɪt/) 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, while dolerite is the preferred name in the rest of the English-speaking world, where sometimes the name diabase refers to altered dolerites and basalts. Some geologists prefer to avoid confusion by using the name microgabbro.

The name diabase comes from the French diabase, and ultimately from the Greek διάβασις diábasis 'act of crossing over, transition', whereas the name dolerite comes from the French dolérite, from the Greek δολερός dolerós 'deceitful, deceptive', because it was easily confused with diorite.