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Diorite ( ) is an formed by the slow cooling underground of (molten rock) that has a moderate content of and a relatively low content of . It is intermediate in composition between low-silica () and high-silica () .

Diorite is found in mountain-building belts ( ) on the margins of continents. It has the same composition as the fine-grained volcanic rock, , which is also common in orogens.

Diorite has been used since prehistoric times as decorative stone. It was used by the of Sargon of Akkad for funerary sculptures, and by many later civilizations for sculptures and building stone.


Description
Diorite is an composed principally of the (typically ), , , and sometimes . The chemical composition of diorite is intermediate, between that of and .
(1996). 9780716724384, W.H. Freeman.
(1997). 9780922152346, American Geological Institute.
It is distinguished from gabbro on the basis of the composition of the plagioclase species; the plagioclase in diorite is richer in and poorer in .
(2025). 9780521880060, Cambridge University Press.

Geologists use rigorous quantitative definitions to classify coarse-grained igneous rocks, based on the mineral content of the rock. For igneous rocks composed mostly of silicate minerals, and in which at least 10% of the mineral content consists of , feldspar, or minerals, classification begins with the . The relative abundances of quartz (Q), (A), plagioclase (P), and feldspathoid (F), are used to plot the position of the rock on the diagram. The rock will be classified as either a dioritoid or a if quartz makes up less than 20% of the QAPF content, feldspathoid makes up less than 10% of the QAPF content, and plagioclase makes up more than 65% of the total feldspar content. Dioritoids are distinguished from gabbroids by an (calcium plagioclase) fraction of their total plagioclase of less than 50%.

The composition of the plagioclase cannot easily be determined , and then a preliminary distinction is made between dioritoid and gabbroid based on the content of mafic minerals. A dioritoid typically has less than 35% mafic minerals, typically including hornblende, while a gabbroid typically has over 35% mafic minerals, mostly pyroxenes or olivine. The name diorite (from italic=no, "to distinguish") was first applied to the rock by René Just Haüy on account of its characteristic, easily identifiable large crystals of hornblende.

Dioritoids form a family of rock types similar to diorite, such as , , or nepheline-bearing diorite. Diorite itself is more narrowly defined, as a dioritoid in which quartz makes up less than 5% of the QAPF content, feldspathoids are not present, and plagioclase makes up more than 90% of the feldspar content.

Diorite may contain small amounts of quartz, , and . , , , , , and occur as accessory minerals. Varieties deficient in hornblende and other dark minerals are called leucodiorite. A ferrodiorite is a dioritoid enriched in and . Ferrodiorites are common in the lower oceanic crust.

Coarse-grained () dioritoids are produced by slow crystallization of having the same composition as the that solidifies rapidly to form fine-grained () . Rock of similar composition to diorite or andesite but with an intermediate texture is sometimes called microdiorite.

(2025). 9780199653065, Oxford University Press.
Diorite is occasionally . It usually contains enough mafic minerals to be dark in appearance.
(1993). 047157452X, Wiley. 047157452X
Orbicular diorite shows alternating concentric growth bands of plagioclase and surrounding a nucleus, within a diorite porphyry matrix.


Occurrence
Diorite results from the of a mafic rock above a . It is found in , and in cordilleran , such as in the . However, while its equivalent, andesite, is common in these settings, diorite is a minor component of the plutonic rocks, which are mostly or granite. Diorite also makes up some stocks intruded beneath large .

Diorite source localities include and , UK; and in Germany; Finland; Romania; central Sweden; southern around Victoria, Canada; Muller, J.E. (1980). Geology Victoria Map 1553A. Ottawa: Geological Survey of Canada the of New Zealand; the Andes Mountains;

(1991). 9780813722658, Geological Society of America.
and Concordia in South Africa. Hornblende diorite is a common rock type in the , , and La Sal Mountains of , US, where it was emplaced as .
(2025). 9781607810049, University of Utah Press.

An orbicular variety found in was formerly called . An obsolete name for microdiorite, markfieldite, was given by Frederick Henry Hatch in 1909 to exposures near the village of , England. is a local name for microdiorite given by Auguste Michel-Lévy to exposures in the Esterel Massif in France.


Use
Human use of diorite dates at least to the , when it was used in a at Le Dolmen du Mont Ubé, . The use of stone of contrasting colour suggests that diorite was deliberately selected for its appearance.

The first great empire, the of Sargon of Akkad, began using diorite for sculpture after sources of the rock came under Akkadian control. Diorite was used to depict rulers or high officials in ceremonial poses or attitudes of prayer, and the sculptures may have been designed to receive funerary offerings.

(2025). 9781317415527, Taylor and Francis.
Diorite was also used for stone vases by craftspeople, who developed considerable skill at polishing diorite and other stones. The Egyptians had become skilled at shaping diorite and other hard stones by 4000 BCE.
(2025). 9783540785934
A large diorite in the dating to 1700 BCE is inscribed with the Code of Hammurabi.
(2025). 9780203930960, Routledge.

Diorite was used by the civilization as structural stone. It was used by medieval Islamic builders to construct water fountains in the . In later times, diorite was commonly used as ; today many diorite cobblestone streets can be found in England and Guernsey. Guernsey diorite was used in the steps of St Paul's Cathedral, London.

(2025). 9781785702785, Oxbow Books.

Today, diorite is uncommon in construction, although it shares similar physical properties with granite. Diorite is often sold commercially as "black granite". Diorite's modern uses include construction aggregate, curbing, usage as , cobblestone, and facing stones.

File:Jar with Lug Handles LACMA M.71.73.54.jpg| jar with lug handles; ; height: ; Los Angeles County Museum of Art (US) File:Gudea of Lagash Girsu.jpg| Statue of Gudea I, dedicated to the god ; 2120 BC (the period); height: , width: , depth: ; File:Weight Shulgi Louvre AO22187.jpg|Weight dedicated by King of Ur with a crescent moon on it; 2094-2047 BC; weight: 248 g; Louvre File:Head of a bearded god wearing a cap with horns dedicated by Puzur-Eshtar of Mari.jpg| head of a bearded god wearing a cap with horns dedicated by Puzur-Eshtar of Mari; middle ; height: ; italic=no (, Germany) File:Head of a Cow Goddess (Hathor or Mehetweret) MET DP311571.jpg|Head of a cow goddess ( or ); 1390-1352 BC; height: , width: , depth: ; Metropolitan Museum of Art (New York City) File:Paris - Toutânkhamon, le Trésor du Pharaon - Amon protégeant Toutânkhamon - 005.jpg|Statue of ; 1336-1327 BC; height: , width: 44, length: ; Louvre File:Block Statue of the God's Father Pameniuwedja, son of Nesmin and Nestefnut MET 07.228.25 EGDP023155.jpg|Block statue of the god's father Pameniuwedja, son of Nesmin and Nestefnut; 4th century BC; height: , width: , depth: ; Metropolitan Museum of Art File:Pair of vases MET DT4387.jpg|Vase with ornaments; ; ; Metropolitan Museum of Art File:Palazzo delle Poste di Napoli - ingresso.jpg|italic=no, Naples, Italy, Gino Franzi, 1936. Modernism, constructed with and diorite.


See also
  • List of rock types


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