Diorite
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Diorite (Template:IPAc-en Template:Respell)Template:RefnTemplate:Refn is an intrusive igneous rock formed by the slow cooling underground of magma (molten rock) that has a moderate content of silica and a relatively low content of alkali metals. It is intermediate in composition between low-silica (mafic) gabbro and high-silica (felsic) granite.
Diorite is found in mountain-building belts (orogens) on the margins of continents. It has the same composition as the fine-grained volcanic rock, andesite, which is also common in orogens.
Diorite has been used since prehistoric times as decorative stone. It was used by the Akkadian Empire of Sargon of Akkad for funerary sculptures, and by many later civilizations for sculptures and building stone.
DescriptionEdit
Diorite is an intrusive igneous rock composed principally of the silicate minerals plagioclase feldspar (typically andesine), biotite, hornblende, and sometimes pyroxene. The chemical composition of diorite is intermediate, between that of mafic gabbro and felsic granite.<ref name=BlattTracy1996>Template:Cite book</ref><ref name=Jackson1997>Template:Cite book</ref> It is distinguished from gabbro on the basis of the composition of the plagioclase species; the plagioclase in diorite is richer in sodium and poorer in calcium.<ref name="lebas-streckeisen-1991">Template:Cite journal</ref><ref name="bgs">Template:Cite journal</ref><ref name=PhilpottsAgue2009>Template:Cite book</ref>
Template:Anchor 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 quartz, feldspar, or feldspathoid minerals, classification begins with the QAPF diagram. The relative abundances of quartz (Q), alkali feldspar (A), plagioclase (P), and feldspathoid (F), are used to plot the position of the rock on the diagram.<ref name="lebas-streckeisen-1991"/><ref name="bgs"/><ref name=PhilpottsAgue2009/> The rock will be classified as either a dioritoid or a gabbroid 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 anorthite (calcium plagioclase) fraction of their total plagioclase of less than 50%.Template:Sfn
The composition of the plagioclase cannot easily be determined in the field, 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.Template:Sfn The name diorite (from Ancient Greek {{#invoke:Lang|lang}}, "to distinguish") was first applied to the rock by René Just Haüy<ref>Template:Oed</ref> on account of its characteristic, easily identifiable large crystals of hornblende.<ref name=Jackson1997/>
Dioritoids form a family of rock types similar to diorite, such as monzodiorite, quartz diorite, 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.Template:Sfn<ref name="lebas-streckeisen-1991"/><ref name="bgs"/>
Diorite may contain small amounts of quartz, microcline, and olivine. Zircon, apatite, titanite, magnetite, ilmenite, and sulfides occur as accessory minerals.Template:Sfn Varieties deficient in hornblende and other dark minerals are called leucodiorite.<ref name="bgs"/><ref>Template:Cite journal</ref> A ferrodiorite is a dioritoid enriched in ironTemplate:Sfn and titanium. Ferrodiorites are common in the lower oceanic crust.<ref>Template:Cite journal</ref>
Coarse-grained (phaneritic) dioritoids are produced by slow crystallization of magma having the same composition as the lava that solidifies rapidly to form fine-grained (aphanitic) andesite.<ref name="lebas-streckeisen-1991"/><ref name="bgs"/> Rock of similar composition to diorite or andesite but with an intermediate texture is sometimes called microdiorite.<ref name=Allaby2013>Template:Cite book</ref> Diorite is occasionally porphyritic.<ref>Template:Cite journal</ref> It usually contains enough mafic minerals to be dark in appearance.<ref name=KleinHurlbut1993>Template:Cite book</ref> Orbicular diorite shows alternating concentric growth bands of plagioclase and amphibole surrounding a nucleus, within a diorite porphyry matrix.<ref>Template:Cite journal</ref>
OccurrenceEdit
Diorite results from the partial melting of a mafic rock above a subduction zone. It is found in volcanic arcs, and in cordilleran mountain building, such as in the Andes Mountains. However, while its extrusive volcanic equivalent, andesite, is common in these settings, diorite is a minor component of the plutonic rocks, which are mostly granodiorite or granite.Template:Sfn Diorite also makes up some stocks intruded beneath large calderas.Template:Sfn
Diorite source localities include Leicestershire<ref>Template:Cite journal</ref> and Aberdeenshire,<ref>Template:Cite journal</ref> UK; Thuringia and Saxony in Germany;<ref>Template:Cite book</ref> Finland;<ref>Template:Cite journal</ref> Romania;<ref>Template:Cite journal</ref> central Sweden;<ref>Template:Cite journal</ref> southern Vancouver Island around Victoria, Canada;<ref> Muller, J.E. (1980). Geology Victoria Map 1553A. Ottawa: Geological Survey of Canada</ref> the Darran Range of New Zealand;<ref name="DarransNZ">Template:Cite journal</ref> the Andes Mountains;<ref name="Andes1991">Template:Cite book</ref> and Concordia in South Africa.<ref>Template:Cite journal</ref> Hornblende diorite is a common rock type in the Henry, Abajo, and La Sal Mountains of Utah, US, where it was emplaced as laccoliths.<ref>Template:Cite book</ref>
An orbicular variety found in Corsica was formerly called corsite.Template:Sfn An obsolete name for microdiorite, markfieldite, was given by Frederick Henry Hatch in 1909 to exposures near the village of Markfield, England.Template:Sfn Esterellite is a local name for microdiorite given by Auguste Michel-Lévy to exposures in the Esterel Massif in France.<ref>Template:Cite journal</ref>
UseEdit
Human use of diorite dates at least to the Middle Neolithic, when it was used in a passage grave at Le Dolmen du Mont Ubé, Jersey. The use of stone of contrasting colour suggests that diorite was deliberately selected for its appearance.<ref>Template:Cite journal</ref>
The first great Mesopotamian empire, the Akkadian Empire 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.<ref>Template:Cite book</ref> Diorite was also used for stone vases by Bronze Age craftspeople, who developed considerable skill at polishing diorite and other stones.<ref>Template:Cite journal</ref> The Egyptians had become skilled at shaping diorite and other hard stones by 4000 BCE.<ref>Template:Cite book</ref> A large diorite stela in the Louvre Museum dating to 1700 BCE is inscribed with the Code of Hammurabi.<ref>Template:Cite book</ref>
Diorite was used by the Inca<ref>Template:Cite journal</ref> civilization as structural stone. It was used by medieval Islamic builders to construct water fountains in the Crimea.<ref>Template:Cite journal</ref> In later times, diorite was commonly used as cobblestone; today many diorite cobblestone streets can be found in England and Guernsey.<ref>Template:Cite journal</ref> Guernsey diorite was used in the steps of St Paul's Cathedral, London.<ref>Template:Cite book</ref>
Today, diorite is uncommon in construction, although it shares similar physical properties with granite. Diorite is often sold commercially as "black granite".<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Diorite's modern uses include construction aggregate, curbing, usage as dimension stones, cobblestone, and facing stones.
- Jar with Lug Handles LACMA M.71.73.54.jpg
Naqada II jar with lug handles; Template:Circa; height: Template:Convert; Los Angeles County Museum of Art (US)
- Gudea of Lagash Girsu.jpg
Statue of Gudea I, dedicated to the god Ningishzida; 2120 BC (the Neo-Sumerian period); height: Template:Convert, width: Template:Convert, depth: Template:Convert; Louvre
- Head of a bearded god wearing a cap with horns dedicated by Puzur-Eshtar of Mari.jpg
lang}} (Berlin, Germany)
- Head of a Cow Goddess (Hathor or Mehetweret) MET DP311571.jpg
Head of a cow goddess (Hathor or Mehet-Weret); 1390-1352 BC; height: Template:Convert, width: Template:Convert, depth: Template:Convert; Metropolitan Museum of Art (New York City)
- Paris - Toutânkhamon, le Trésor du Pharaon - Amon protégeant Toutânkhamon - 005.jpg
Statue of Amun; 1336-1327 BC; height: Template:Convert, width: 44Template:Clarify, length: Template:Convert; Louvre
- 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: Template:Convert, width: Template:Convert, depth: Template:Convert; Metropolitan Museum of Art
- Pair of vases MET DT4387.jpg
Vase with gilt bronze ornaments; Template:Circa; Template:Convert; Metropolitan Museum of Art
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