Tasmania is an island state, part of the Commonwealth of Australia, located 240 kilometres to the south of the Australian continent, separated by Bass Strait. The state includes the island of Tasmania, the 26th largest island in the world, and the surrounding 334 islands.The state has a population of 507,626, of whom almost half reside in the greater Hobart precinct. Tasmania's area is 68,401 square kilometres, of which the main island covers 62,409 square kilometres.Tasmania is promoted as the natural state, the "Island of Inspiration",and A World Apart, Not A World Away owing to its large and relatively unspoiled natural environment. Almost 45% of Tasmania lies in reserves, national parks and World Heritage Sites.The island is 364 kilometres long from its northernmost to its southernmost points, and 306 kilometres from west to east.The state capital and largest city is Hobart, which encompasses the local government areas of City of Hobart, City of Glenorchy, and City of Clarence, while the satellite town of Kingston is generally included in the Greater Hobart area.The northernmost terrestrial point of the state of Tasmania is Boundary Islet, a nature reserve in Bass Strait which, due to a quirk of history, is shared with the state of Victoria.The subantarctic Macquarie Island and its surrounding islands are also under the administration of Tasmania as a nature reserve and part of the Huon Valley Council local government area. The Bishop and Clerk Islets, about 37 km south of Macquarie Island, are the southernmost terrestrial point of the state of Tasmania, and the southernmost internationally recognised land in Australia.The island was adjoined to the mainland of Australia until the end of the last glacial period approximately 10,000 years ago. Much of the island is composed of Jurassic dolerite intrusions through other rock types, sometimes forming large columnar joints. Tasmania has the world's largest areas of dolerite, with many distinctive mountains and cliffs formed from this rock type.The central plateau and the southeast portions of the island are mostly dolerite. Mount Wellington above Hobart is a good example, showing distinct columns known as the Organ Pipes. In the southern midlands as far south as Hobart, the dolerite is underlaid by sandstone and similar sedimentary stones. In the southwest, Precambrian quartzites was formed from very ancient sea sediments and form strikingly sharp ridges and ranges, such as Federation Peak or Frenchmans Cap.In the northeast and east, continental granites can be seen, such as at Freycinet, similar to coastal granites on mainland Australia. In the northwest and west, mineral-rich volcanic rock can be seen at Mount Read near Rosebery, or at Mount Lyell near Queenstown. Also present in the south and northwest is limestone with magnificent caves.The quartzite and dolerite areas in the higher mountains show evidence of glaciation, and much of Australia's glaciated landscape is found on the Central Plateau and the Southwest. Cradle Mountain, another dolerite peak, for example, was a nunatak. The combination of these different rock types offers incredible scenery, much of it distinct from any other region of the world. In the far southwest corner of the state, the geology is almost completely quartzite, which gives the mountains the false impression of having snow-capped peaks year round.