Diorite Rock Type, Composition, Formation, Occurrence & Uses

Diorite Rock
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Diorite is a coarse-grained intrusive igneous rock. Its composition is in-between granite and basalt. The rock is usually found as large intrusions, dikes, and sills.


Rock Composition

Diorite is composed of silicate minerals like plagioclase feldspar (typically andesine), biotite, hornblende, and/or pyroxene. Diorite may also contain trace amounts of microcline, quartz, and olivine. Sulfides, zircon, apatite, titanite, magnetite, and ilmenite are accessory minerals in diorite.

The rock is classified as dioritoid or a gabbroid if the quartz content is less than 20%, feldspathoid is less than 10%, and plagioclase is more than 65% of the total feldspar content.

diagram with dioritoid fields highlighted in yellow and diorite in red
diagram with dioritoid fields highlighted in yellow and diorite in red

Diorite Rock Formation

Diorite is formed due to the partial melting of a mafic rock above a subduction zone. This melting produces a basaltic magma that rises and intrudes into the continental plate’s granite rock. The basaltic magma mixes with granitic magma and melts granitic rocks, ascending through the continental plate.

This process results in the formation of melt in-between basalt and granite. Diorite forms when this melt crystallizes and cools.

Where is Diorite Found?

Diorite is found abundantly at following places.

  • Leicestershire and Aberdeenshire, UK
  • Thuringia and Saxony in Germany
  • Finland
  • Romania
  • Central Sweden
  • Southern Vancouver Island, near Victoria, British Colombia, Canada
  • Darran Range in New Zealand
  • Andes Mountains, western edge, South America
  • Concordia, South Africa
  • Henry and La Sal Mountains, Utah

Diorite Uses

Diorite is used as a crushed stone for base material in road construction, buildings, and parking lots. Its durability is similar to granite and trap rock. Diorite is often used as a drainage stone and for erosion control.

Mineral assemblage of igneous rocks
Mineral assemblage of igneous rocks

Diorite is also used in the dimension stone industry for facing stones, tiles, blocks, pavements, curbing, and other dimension stone products. Polished diorite is also used as architectural stone. Inca and Mayan civilizations, ancient civilizations in the Middle East, used diorite as a structural stone.

Diorite Sculptures

Naqada II jar with lug handles; c. 3500–3050 BC; height: 13 cm; Los Angeles County Museum of Art (US)

Statue of Gudea I, dedicated to the god Ningishzida; 2120 BC (the Neo-Sumerian period)

Palazzo delle Poste di Napoli, Gino Franzi, 1936. A masterpiece of modernism, constructed with marble and diorite.

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