Granites are a plutonic igneous rock, forming from magma deep within the Earths crust. They contain large visible mineral crystals due to slowly cooling over time and represent the magma chambers of ancient volcanoes.
Granites come in many different looking forms and colours but all contain quartz, alkali and plagioclase feldspars, as well as often containing silver muscovite mica, black biotite mica or amphiboles. Veins of pegmatite often cut through these magma chambers as a late-stage feature when the chamber has almost all finished crystallising and turning to rock. A pegmatite is a rock made of ginormous crystals, usually a few centimetres long, but sometimes, like in the photograph, many metres in size!
Granites are common on Te Tai Poutini West Coast, representing a time in Zealandias history when great magma chambers cooled slowly deep within the Earth, just prior to the rifting away from the supercontinent, Gondwana. The large interlocking crystals formed from this slow process makes the rocks hard and resistant to erosion, making prominent hills along the West Coast, sticking proud out of the more recently glaciated landscape. These rocks are generally around 100 to 150 million years old.
