Diorite ( ) is an
intrusive igneous rock formed by the slow cooling underground of
magma
Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natura ...
(molten rock) that has a moderate content of
silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...
and a relatively low content of
alkali metals. It is
intermediate in composition between low-silica (
mafic
A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks in ...
)
gabbro
Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is ...
and high-silica (
felsic)
granite
Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies un ...
.
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
The Akkadian Empire () was the first ancient empire of Mesopotamia after the long-lived civilization of Sumer. It was centered in the city of Akkad () and its surrounding region. The empire united Akkadian and Sumerian speakers under one r ...
of
Sargon of Akkad for funerary sculptures, and by many later civilizations for sculptures and building stone.
Description
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
A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks in ...
gabbro
Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is ...
and
felsic granite
Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies un ...
.
It is distinguished from gabbro on the basis of the composition of the plagioclase species; the plagioclase in diorite is richer in
sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...
and poorer in
calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...
.
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
Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) feldspa ...
(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 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%.
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. The name ''diorite'' (from ]Ancient Greek
Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic pe ...
, "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 ]monzodiorite Monzodiorite is an intrusive rock with a composition intermediate between diorite and monzonite. It is defined in the QAPF classification as coarse-grained igneous rock in which quartz
Quartz is a hard, crystalline mineral composed of silica ( ...
, quartz diorite
Quartz diorite is an igneous, plutonic ( intrusive) rock, of felsic composition, with phaneritic texture. Feldspar is present as plagioclase (typically oligoclase or andesine) with 10% or less potassium feldspar. Quartz is present at between 5 an ...
, or nepheline-bearing diorite Nepheline-bearing diorite is an intrusive rock
Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form '' intrusions'', such as batholiths, dikes, sills, laccoliths, and volcanic necks. ...
. 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, microcline
Microcline (KAlSi3O8) is an important igneous rock-forming tectosilicate mineral. It is a potassium-rich alkali feldspar. Microcline typically contains minor amounts of sodium. It is common in granite and pegmatites. Microcline forms durin ...
, and olivine
The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers qui ...
. Zircon, apatite, titanite, magnetite, ilmenite, and sulfides
Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds la ...
occur as accessory minerals. Varieties deficient in hornblende and other dark minerals are called ''leucodiorite''. A ''ferrodiorite'' is a dioritoid enriched in iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
and titanium. Ferrodiorites are common in the lower oceanic crust The lower oceanic crust is the lower part of the oceanic crust and represents the major part of it (volumetrically biggest part). It is generally located 4–8 km below the ocean floor and the major lithologies are mafic (ultramafic and gabbro ...
.
Coarse-grained ( phaneritic) dioritoids are produced by slow crystallization of magma
Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natura ...
having the same composition as the lava that solidifies rapidly to form fine-grained (aphanitic
Aphanites (adj. ''aphanitic''; ) are igneous rocks that are so fine-grained that their component mineral crystals are not visible to the naked eye (in contrast to phanerites, in which the crystals are visible to the unaided eye). This ge ...
) andesite. Rock of similar composition to diorite or andesite but with an intermediate texture is sometimes called ''microdiorite''. Diorite is occasionally porphyritic. It usually contains enough mafic minerals to be dark in appearance. ''Orbicular diorite'' shows alternating concentric growth bands of plagioclase and amphibole surrounding a nucleus, within a diorite porphyry matrix
Matrix most commonly refers to:
* ''The Matrix'' (franchise), an American media franchise
** '' The Matrix'', a 1999 science-fiction action film
** "The Matrix", a fictional setting, a virtual reality environment, within ''The Matrix'' (franchi ...
.
Occurrence
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
Mountain formation refers to the geological processes that underlie the formation of mountains. These processes are associated with large-scale movements of the Earth's crust (tectonic plates). Folding, faulting, volcanic activity, igneous intr ...
, 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. Diorite also makes up some stocks intruded beneath large calderas.
Diorite source localities include Leicestershire and Aberdeenshire, UK; Thuringia
Thuringia (; german: Thüringen ), officially the Free State of Thuringia ( ), is a state of central Germany, covering , the sixth smallest of the sixteen German states. It has a population of about 2.1 million.
Erfurt is the capital and lar ...
and Saxony
Saxony (german: Sachsen ; Upper Saxon German, Upper Saxon: ''Saggsn''; hsb, Sakska), officially the Free State of Saxony (german: Freistaat Sachsen, links=no ; Upper Saxon: ''Freischdaad Saggsn''; hsb, Swobodny stat Sakska, links=no), is a ...
in Germany; Finland; Romania; central Sweden; southern Vancouver Island around Victoria, Canada; the Darran Range
The Darran Mountains are a prominent range within New Zealand's Fiordland National Park, the country's biggest national park. They contain the park's highest peak, Mount Tūtoko ().
The range lies between Milford Sound (Piopiotahi) and the valley ...
of New Zealand; the Andes Mountains; and Concordia in South Africa. Hornblende diorite is a common rock type in the Henry, Abajo, and La Sal Mountains
The La Sal Mountains or La Sal Range are a mountain range located in Grand and San Juan counties in the U.S. state of Utah, along the border with Colorado. The range rises above and southeast of Moab and north of the town of La Sal. This range ...
of Utah, US, where it was emplaced as laccoliths.
An orbicular Orbicular is an adjective meaning "circular"
Orbicular may also refer to:
* Orbicular leaf, a plant leaf shape
* Orbicularis oculi muscle, a muscle around the eye
* Orbicularis oris muscle, a muscle around the mouth
* Orbicular batfish, a spec ...
variety found in Corsica was formerly called '' corsite''. An obsolete name for microdiorite, ''markfieldite'', was given by Frederick Henry Hatch in 1909 to exposures near the village of Markfield
Markfield is a large village in both the National Forest and Charnwood Forest and in the Hinckley and Bosworth district of Leicestershire, England. The settlement dates back to at least the time of the Norman conquest and is mentioned in the ...
, England.
Use
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.
The first great Mesopotamia
Mesopotamia ''Mesopotamíā''; ar, بِلَاد ٱلرَّافِدَيْن or ; syc, ܐܪܡ ܢܗܪ̈ܝܢ, or , ) is a historical region of Western Asia situated within the Tigris–Euphrates river system, in the northern part of the ...
n empire, the Akkadian Empire
The Akkadian Empire () was the first ancient empire of Mesopotamia after the long-lived civilization of Sumer. It was centered in the city of Akkad () and its surrounding region. The empire united Akkadian and Sumerian speakers under one r ...
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. Diorite was also used for stone vases by Bronze Age
The Bronze Age is a historic period, lasting approximately from 3300 BC to 1200 BC, characterized by the use of bronze, the presence of writing in some areas, and other early features of urban civilization. The Bronze Age is the second pri ...
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. A large diorite stela in the Louvre Museum dating to 1700 BCE is inscribed with the Code of Hammurabi.
Diorite was used by the Inca civilization as structural stone. It was used by medieval Islamic builders to construct water fountains in the Crimea
Crimea, crh, Къырым, Qırım, grc, Κιμμερία / Ταυρική, translit=Kimmería / Taurikḗ ( ) is a peninsula in Ukraine, on the northern coast of the Black Sea, that has been occupied by Russia since 2014. It has a p ...
. In later times, diorite was commonly used as cobblestone; 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.
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 dimension stones, cobblestone, and facing stones.
File:Jar with Lug Handles LACMA M.71.73.54.jpg, Naqada II 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 Ningishzida; 2120 BC (the Neo-Sumerian period); height: , width: , depth: ; Louvre
File:Weight Shulgi Louvre AO22187.jpg, Weight dedicated by King Shulgi 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, Assyrian head of a bearded god wearing a cap with horns dedicated by Puzur-Eshtar of Mari; middle Bronze Age
The Bronze Age is a historic period, lasting approximately from 3300 BC to 1200 BC, characterized by the use of bronze, the presence of writing in some areas, and other early features of urban civilization. The Bronze Age is the second pri ...
; height: ; (Berlin
Berlin ( , ) is the capital and largest city of Germany by both area and population. Its 3.7 million inhabitants make it the European Union's most populous city, according to population within city limits. One of Germany's sixteen constitu ...
, Germany)
File:Head of a Cow Goddess (Hathor or Mehetweret) MET DP311571.jpg, Head of a cow goddess ( Hathor or Mehet-Weret); 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 Amun; 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 gilt bronze
Ormolu (; from French ''or moulu'', "ground/pounded gold") is the gilding technique of applying finely ground, high-carat gold– mercury amalgam to an object of bronze, and for objects finished in this way. The mercury is driven off in a kil ...
ornaments; ; ; Metropolitan Museum of Art
File:Palazzo delle Poste di Napoli - ingresso.jpg, , Naples, Italy, Gino Franzi, 1936. Modernism
Modernism is both a philosophical and arts movement that arose from broad transformations in Western society during the late 19th and early 20th centuries. The movement reflected a desire for the creation of new forms of art, philosophy, an ...
, constructed with marble and diorite.
See also
* List of rock types
References
External links
{{Authority control
Granitic rocks
Intermediate rocks
Plutonic rocks