Norite: Difference between revisions

'''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 [[clinopyroxene]]s, generally medially iron-rich [[augite]]s.<ref>Carmichael, Turner and Verhoogen, 1974, Igneous Petrology, McGraw-Hill, pp. 603–620</ref><ref>Hyndman, Donald W., 1972, ''Igneous and Metamorphic Petrology,'' McGraw-Hill, pp. 122–139, esp. references.</ref>

Norite occurs with gabbro and other mafic to [[ultramafic]] rocks in [[layered intrusion]]s which are often associated with [[platinum]] [[ore]]bodies such as in the Bushveld Igneous Complex in [[South Africa]], the [[Skaergaard intrusion|Skaergaard igneous complex]] of [[Greenland]], and the [[Stillwater igneous complex]] in [[Montana]], [[USA]]. Norite is also the basal igneous rock of the [[Sudbury Basin]] complex in [[Ontario]], which is the site of a [[impact event|meteorite impact]] and the world's second-largest [[nickel]] mining region. Norite is a common rock type of the [[Moon rock|Apollo samples]]. On a smaller scale, norite can be found in small localized [[intrusion]]s such as the Gombak Norite in [[Bukit Gombak]], [[Singapore]]. It is also plentiful in the [[Egersund]] intrusion area of southwestern [[Norway]], with [[titanium]] deposits to the east.