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Diorite is an intrusive igneous rock composed principally of the silicate minerals plagioclase feldspar (typically andesine), biotite, hornblende, and sometimes pyroxene.The chemical composition of diorite is intermediate, between that of mafic gabbro and felsic granite.
Quartz diorite from Dúbrava, Nízke Tatry Mountains, Slovakia. Quartz diorite is an igneous, plutonic rock, of felsic composition, with phaneritic texture. Feldspar is present as plagioclase (typically oligoclase or andesine) with 10% or less potassium feldspar. Quartz is present at between 5 and 20% of the rock.
Monzodiorite – igneous rock An intrusive igneous rock intermediate in composition between diorite and monzonite Monzogranite – Biotite granite rocks that are considered to be the final fractionation product of magma – A silica-undersaturated granite with <5% normative quartz
Napoleonite is a variety of diorite which is characterized by orbicular structure. The grey matrix of the stone has the normal appearance of a diorite, but contains many rounded lumps 1 or 2 inches in diameter, which show concentric zones of light and dark colors.
This rock can be observed to transition into diorite by changes in the mineral content and texture. Layered gabbro has also been changed into diorite at Le Nez point, the southernmost point of the main island. The diorite is emplaced at and near Sorel point, and at several places along the south coast east of Saint Helier. It also is found on ...
Quartz (SiO 2) is present as more than 20% of the total quartz-alkali feldspar-plagioclase-feldspathoid content of the rock. [1] [2] Amphiboles and biotite are common in lesser quantities, while accessory minerals include apatite, magnetite and zircon. [3] [4] In older references tonalite is sometimes used as a synonym for quartz diorite.
Iron-rich felsic rocks, including monzonite and rapakivi granite; Iron-rich diorite, gabbro, and norite; Leucocratic mafic rocks such as leucotroctolite and leuconorite; Though co-eval, these rocks likely represent chemically-independent magmas, likely produced by melting of country rock into which the anorthosites intruded. [2]
Hornblende diorite from the Henry Mountains, Utah, US. Hornblende is a common constituent of many igneous and metamorphic rocks such as granite, syenite, diorite, gabbro, basalt, andesite, gneiss, and schist. It crystallizes in preference to pyroxene minerals from cooler magma that is richer in silica and water. [13]