page_title: Diorite
section_title: Occurrence
hierarchical_section_title: Diorite / Occurrence
caption_attribution_description: Galego: Diorita&#160;
context_page_description: Diorite is an intrusive igneous rock composed principally of the silicate minerals plagioclase feldspar, biotite, hornblende, and/or pyroxene. The chemical composition of diorite is intermediate, between that of mafic gabbro and felsic granite. Diorite is usually grey to dark-grey in color, but it can also be black or bluish-grey, and frequently has a greenish cast. It is distinguished from gabbro based on the composition of the plagioclase species; the plagioclase in diorite is richer in sodium and poorer in calcium. Diorite may contain small amounts of quartz, microcline, and olivine. Zircon, apatite, titanite, magnetite, ilmenite, and sulfides occur as accessory minerals. Minor amounts of muscovite may also be present. Varieties deficient in hornblende and other dark minerals are called leucodiorite. When olivine and more iron-rich augite are present, the rock grades into ferrodiorite, which is transitional to gabbro. The presence of significant quartz makes the rock type quartz-diorite or tonalite, and if orthoclase is present at greater than 10 percent, the rock type grades into monzodiorite or granodiorite.
context_section_description: Diorite is a relatively rare rock; source localities include Leicestershire (one name for microdiorite—markfieldite—exists due to the rock's being found in the village of Markfield) and Aberdeenshire, UK; Guernsey; Sondrio, Italy; Thuringia and Saxony in Germany; Finland; Romania; Northeastern Turkey; central Sweden; the Darrans range of New Zealand; the Andes Mountains.
  An orbicular variety found in Corsica is called corsite.
caption: Diorite
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