Under large areas of the mountains in north-west Nelson lies coarse-grained granite, named Karamea Granite, similar to this slab. The large pink crystals (up to 2 centimetres long) are potassium feldspar; the white crystals are plagioclase feldspar; the grey glassy grains are quartz; and the black grains are biotite. These four minerals are the typical constituents of granite. Radiometric dating of Karamea Granite has shown that it formed about 375 million years ago, in the late Devonian period.