Tasmania is dominated by the rock dolerite: 1500 cubic kilometres of it. When the Gondwana supercontinent fragmented into Europe, Asia, the Americas, Africa, Australia and Antarctica in the Jurassic era (about 165 million years ago), the fractures resulted in enormous outpourings of basalt, not only along the spreading axes now seen as mid-oceanic ridges in our oceans but along transverse faults extending into the continents where we now see the continental flood basalts. These are now termed the Ferrar Dolerites and Volcanics in Antarctica, the Tasmanian Dolerites in Australia, the Deccan Traps in India, (mainly basalts), the Parana Basalts in southern Brazil, the Karoo Dolerites in South Africa, the Hebridean Province of the British Tertiary in western Scotland and northern Ireland, the Palisades Sill and related intrusions found in eastern USA., and the Flood basalts of East and West Greenland.
This photo shows the cliff of southern Bruny Island. Not the best example of the wonderful columnar jointing you get in these parts, but I just loved the dice-like joints that fracture the rock face.