GraniteGranite is a felsic, generally equigranular, relatively light coloured intrusive rock. It comprises some of the oldest known rocks on Earth, and is the most abundant basement rock underlying the relatively thin sedimentary rock cover of the continents. Granite is produced in volcanic arcs, and more commonly in mountain building resulting from the collision of two continental masses. The earliest continental masses were products of the accumulation of volcanic arcs, and this is why granite lies in the cores of all of the continents. Granite is the plutonic equivalent of rhyolite.
Other specimens - Click the thumbnails to enlarge
Colour - variable but typically light-coloured.
Texture - phaneritic (medium to coarse grained).
Mineral content - orthoclase, plagioclase and quartz (generally more orthoclase than plagioclase), often with smaller amounts of biotite, muscovite or amphibole ( hornblende).
Silica (SiO 2) content - 69%-77%.
Uses - can be used as aggregate, fill etc. in the construction and roading industries (often not ideal for concrete aggregate because of high silica content); cut and polished for dimension stone for building facings, foyers etc; cut and polished for bench tops and counters; cut and carved into monuments, headstones, statues etc.
New Zealand occurrences - west Nelson area, Westland, Fiordland, Stewart Island.