Anorthosite is a phaneritic, intrusive igneous rock which is characterized by a predominance of plagioclase feldspar which is almost 90–100%, and a minimal mafic component.
The banded iron layers are formed in sea water when oxygen is released by photosynthetic cyano-bacteria. The oxygen then combines with dissolved iron in ocean to form insoluble iron oxides, which precipitated out, forming a thin layer of banded iron formation on ocean floor.