Colour Speckled black and white in hand specimen; occasionally shades of dark green or pink. The dark minerals are more noticeable than in gabbro. Colour index 40 to 90, but very variable, often over short distances. Grain size Coarse, may be pegmatitic. Texture Equigranular or porphyritic. In porphyritic varieties the feldspar or hornblende may form phenocrysts. Diorites often vary rapidly in texture; an equigranular variety may grade into a porphyritic one within a few centimetres. They are sometimes foliated due to the roughly parallel arrangement of the minerals. Structure Xenoliths are common. Mineralogy Essentially plagioclase (oligoclase or andesine) and hornblende; biotite and/or pyroxene may occur. Alkali feldspar and quartz (quartz diorites) may be present, when diorite grades into granodiorite. Common accessory minerals are apatite, titanite and iron oxides. Field relations Forms independent stocks, bosses and dykes, but also comprises local variants of masses of granite, and sometimes gabbro, into which they merge imperceptibly.
A coarse-grained plutonic igneous rock of intermediate composition. It consists mainly of plagioclase feldspar and ferromagnesian minerals...
n 1 a dark coarse-grained igneous plutonic rock consisting of plagioclase feldspar and ferromagnesian minerals such as hornblende [C19: from French
1. a granular igneous rock consisting essentially of plagioclase feldspar and hornblende. Plural: diorites Etymology: French, from Greek dior(ize