dioriet

Dioriet is a coarse-grained, intrusive igneous rock. In English geology the standard name is diorite; "dioriet" is a variant spelling used in some languages and older literature. It forms when intermediate-silica magma crystallizes slowly at depth, producing a phaneritic texture with mineral crystals large enough to see with the naked eye.

The typical mineral assemblage consists mainly of plagioclase feldspar, with dark mafic minerals such as hornblende or augite. Quartz is usually sparse or absent, which helps distinguish dioriet from granites and granodiorites. The texture is equigranular, though grain size can vary from a few millimeters to several centimeters in large plutons.

Dioriet is a plutonic rock, formed at considerable depth in crustal settings. It lies compositionally between felsic granites and mafic gabbros and commonly associates with ancient active margins and continental collision zones. It commonly occurs in large plutons and batholiths, either as a primary component or through mingling with other magmas.

Geographic occurrence is widespread, with well-known outcrops in ancient mountain belts and crustal blocks around the world. In North America, diorite-like rocks are exposed in parts of the Adirondack Mountains; in Europe, similar rocks occur in Scotland and the Bohemian Massif. Economically, dioriet is quarried as a dimension stone and used in construction and decorative applications where a durable, medium-color material is desired.

Identification relies on its phaneritic texture, subdued quartz content, and mineral assemblage dominated by plagioclase with hornblende or pyroxene. It is distinguishable from granite by low quartz content and from gabbro by its feldspar- and hornblende-dominant composition and lighter color mottling.