Anorthosite is a phaneritic, intrusive igneous rock characterized by a predominance of plagioclase feldspar (90–100%), and a minimal mafic component (0–10%) including Pyroxene, ilmenite, magnetite, and olivine. Anorthosite can be divided into two main types according to age. Proterozoic & Archaen. This example from Western Norway falls into the former group. Most anorthosite plutons are very coarse grained; that is, the individual plagioclase crystals and the accompanying mafic mineral are greater than a few centimeters long. However, most Proterozoic anorthosites are deformed, and such large plagioclase crystals have recrystallized to form smaller crystals, leaving only the outline of the larger crystals behind.