Diorite

The term Diorite derives from the greek "Dioritas" (to distinguish, separate) to indicate a rock "with sialic and femic portions well distinct"; the term was used for the first time by RJ Hauy in 1822 that used it to describe a rock formed by a white mineral (feldspar) and a dark mineral (amphibole or pyroxene). hereinafter J.F.L. Haussmann and G. Rose limited the use of the term to a rock essentially plagioclase-anfibolic in composition.

Diorite is a coarse-grained, intrusive igneous rock that is intermediate in composition between granite and gabbro. Diorite is composed primarily of plagioclase feldspar, amphibole, and pyroxine minerals with small amounts of biotite mica. It typically contains very little quartz. Zircon, apatite, sphene, magnetite, ilmenite and sulfides occur as accessory minerals. 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 (>5% quartz) or tonalite (>20% quartz), and if orthoclase (potassium feldspar) is present at greater than ten percent the rock type grades into monzodiorite or granodiorite.

Diorites may be associated with either granite or gabbro intrusions, into which they may subtly merge. Diorite results from partial melting of a mafic rock above a subduction zone. It is commonly produced in volcanic arcs, and in cordilleran mountain building such as in the Andes Mountains as large batholiths. The extrusive volcanic equivalent rock type is andesite. An orbicular variety found in Corsica is called corsite.



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QAPF Diagram Diorite field in blue



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Diorite with Garnet. Gore Mountain, New York. From Natalie Teager, Arizona State University.



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Diorite. Gore Mountain, New York. From Natalie Teager, Arizona State University.



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Diorite sample.



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Orbicular Diorite (Corsite). From da Dirk Wiersma





Bibliography



• Ron H. Vernon (2004): A pratical guide to rock microstructure. Cambridge editore
• Eric A.K.Middlemost (1985): Magmas and Magmatic Rocks. Longman, London
Fine art America


Photo
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Green Hornblende and Plagioclase alterd by Sericite in a Diorite from Ilmenau, Thuringen (Germany). PPL image, 2x (Field of view = 7mm)
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Green Hornblende and Plagioclase alterd by Sericite in a Diorite from Ilmenau, Thuringen (Germany). PPL image, 2x (Field of view = 7mm)
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Green Hornblende and Plagioclase alterd by Sericite in a Diorite from Ilmenau, Thuringen (Germany). PPL image, 2x (Field of view = 7mm)
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Green Hornblende and Plagioclase alterd by Sericite in a Diorite from Ilmenau, Thuringen (Germany). XPL image, 2x (Field of view = 7mm)
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Green Hornblende and Plagioclase alterd by Sericite in a Diorite from Ilmenau, Thuringen (Germany). PPL image, 2x (Field of view = 7mm)
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Green Hornblende and Plagioclase alterd by Sericite in a Diorite from Ilmenau, Thuringen (Germany). XPL image, 2x (Field of view = 7mm)
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Green Hornblende and Plagioclase alterd by Sericite in a Diorite from Ilmenau, Thuringen (Germany). XPL image, 2x (Field of view = 7mm)
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Green Hornblende and Plagioclase alterd by Sericite in a Diorite from Ilmenau, Thuringen (Germany). PPL image, 2x (Field of view = 7mm)
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Brown Hornblende and Plagioclase in a Diorite. PPL image, 2x (Field of view = 7mm)
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Brown Hornblende and Plagioclase in a Diorite. XPL image, 2x (Field of view = 7mm)
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Brown Hornblende and Plagioclase in a Diorite. PPL image, 2x (Field of view = 7mm)
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Brown Hornblende and Plagioclase in a Diorite. XPL image, 2x (Field of view = 7mm)
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Brown Hornblende and Plagioclase in a Diorite. PPL image, 2x (Field of view = 7mm)
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Brown Hornblende and Plagioclase in a Diorite. PPL image, 2x (Field of view = 7mm)
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Brown Hornblende and Plagioclase in a Diorite. XPL image, 2x (Field of view = 7mm)