Granite is a common and widely-occurring group of
intrusive folic igneous rocks that form at great depths
and pressures under continents. Granite consists of
orthoclase and plagioclase feldspars, quartz, hornblende,
biotitic, muscovite and minor accessory minerals such as
magnetite, garnet, zircon and apatite. Rarely, a pyroxene
is present. Ordinary granite always carries a small amount
of plagioclase, but when this is absent the rock is
referred to as alkali granite. An increasing proportion of
plagioclase feldspar causes granite to pass into
grandiosity.
Granite