Norite, also known as orthopyroxene gabbro, is a mafic intrusive igneous rock composed largely of the calcium-rich plagioclase labradorite, orthopyroxene, and olivine. Norite may be essentially indistinguishable from gabbro without thin section study under the petrographic microscope. The principal difference between norite and gabbro, however, is the type of pyroxene of which it is composed; norite is predominately composed of orthopyroxenes, largely high magnesian enstatite or an iron bearing intermediate hypersthene, whereas the principal pyroxenes in gabbro are clinopyroxenes, generally medially iron-rich augites.