Geology: Jurassic Dolerite

Tasmania has the largest exposure of dolerite in the world of 30000 km2 and a volume of 15000 km3. In Tasmania the rock is characteristic of many mountains with its columnar joining and dark blue grey colour.

A giant intrusion of magma happened in the Jurassic forming diabase, or dolerite which gives many of the Tasmanian mountains their characteristic appearance. Tasmania has the world's largest areas of dolerite.

Diabase (pronounced /ˈdaɪ.əbeɪs/) or dolerite 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).