Jump to content

Diorite: Difference between revisions

From Wikipedia, the free encyclopedia
Content deleted Content added
changed "salt and pepper" to "speckled"; removed "somewhat"; changed "porphyry" to "porphyritic" and added wiki ink
adde qwiki links for "sodium", "calcium" and "matrix"
Line 6: Line 6:
'''Diorite''' ({{IPAc-en|ˈ|d|aɪ|ər|ˌ|aɪ|t}} or {{IPAc-en|ˈ|d|aɪ|ɵ|ˌ|r|aɪ|t}}) is a grey to dark-grey intermediate [[Intrusion (geology)|intrusive]] [[igneous rock]] composed principally of the [[mineral]]s [[plagioclase]] [[feldspar]] (typically [[andesine]]), [[biotite]], [[hornblende]], and/or [[pyroxene]]. It is distinguished from [[gabbro]] on the basis of the composition of the plagioclase species, where average [[anorthite]] content of plagioclase in a diorite is less than 50 per cent. It may contain small amounts of [[quartz]], [[microcline]], and [[olivine]]. [[Zircon]], [[apatite]], [[titanite]], [[magnetite]], [[ilmenite]], and [[Sulfide mineral|sulfides]] occur as accessory minerals.<ref>Blatt, Harvey and Robert J. Tracy (1996) ''Petrology,'' W. H. Freeman, 2nd edition, p. 53 ISBN 0-7167-2438-3</ref> It can also be black or bluish-grey, and frequently has a greenish cast. 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]]. Diorite has a medium grain size texture and is occasionally [[Porphyry (geology)|porphyritic]].
'''Diorite''' ({{IPAc-en|ˈ|d|aɪ|ər|ˌ|aɪ|t}} or {{IPAc-en|ˈ|d|aɪ|ɵ|ˌ|r|aɪ|t}}) is a grey to dark-grey intermediate [[Intrusion (geology)|intrusive]] [[igneous rock]] composed principally of the [[mineral]]s [[plagioclase]] [[feldspar]] (typically [[andesine]]), [[biotite]], [[hornblende]], and/or [[pyroxene]]. It is distinguished from [[gabbro]] on the basis of the composition of the plagioclase species, where average [[anorthite]] content of plagioclase in a diorite is less than 50 per cent. It may contain small amounts of [[quartz]], [[microcline]], and [[olivine]]. [[Zircon]], [[apatite]], [[titanite]], [[magnetite]], [[ilmenite]], and [[Sulfide mineral|sulfides]] occur as accessory minerals.<ref>Blatt, Harvey and Robert J. Tracy (1996) ''Petrology,'' W. H. Freeman, 2nd edition, p. 53 ISBN 0-7167-2438-3</ref> It can also be black or bluish-grey, and frequently has a greenish cast. 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]]. Diorite has a medium grain size texture and is occasionally [[Porphyry (geology)|porphyritic]].


The [[phaneritic]] speckled [[Rock microstructure|texture]] common to diorite is due to random distribution of medium-sized grains of the white [[albite]] and black or nearly black color amphibole and pyroxene crystals, with minor glints of [[biotite]]. The common silicate mineral assemblage mainly includes sodium rich plagioclase with calcium plagioclase, amphibole, pyroxene, and biotite. Minor amounts of muscovite and quartz, and oxides, such as magnetite and ilmenite, may also be present. A dioritic rock containing [[feldspathoid]] mineral/s while absent of [[quartz]] is termed foid-bearing or foid diorite according to content. Diorite may also be porphyritic. Orbicular diorite shows several alternating concentric growth bands of plagioclase and amphibole surrounding a nucleus within a diorite porphyry matrix.
The [[phaneritic]] speckled [[Rock microstructure|texture]] common to diorite is due to random distribution of medium-sized grains of the white [[albite]] and black or nearly black color amphibole and pyroxene crystals, with minor glints of [[biotite]]. The common [[Silicate minerals|silicate mineral]] assemblage mainly includes [[sodium]]-rich plagioclase, [[calcium]]-rich plagioclase, amphibole, pyroxene, and biotite. Minor amounts of muscovite and quartz, and oxides, such as magnetite and ilmenite, may also be present. A dioritic rock containing [[feldspathoid]] mineral/s while absent of [[quartz]] is termed foid-bearing or foid diorite according to content. Diorite may also be [[Porphyry (geology)|porphyritic]]. Orbicular diorite shows alternating concentric growth bands of plagioclase and amphibole surrounding a nucleus within a diorite porphyry [[Matrix (geology|matrix]].


Diorites may be associated with either [[granite]] or [[gabbro]] [[intrusion]]s, into which they may subtly merge. Diorite results from the [[partial melting]] of a [[mafic]] rock above a [[subduction zone]]. It is commonly produced in [[volcanic arc]]s, and in cordilleran [[orogeny|mountain building]], such as in the [[Andes Mountains]], as large [[batholith]]s. The [[Extrusive (geology)|extrusive]] [[volcanic]] equivalent rock type is [[andesite]].
Diorites may be associated with either [[granite]] or [[gabbro]] [[intrusion]]s, into which they may subtly merge. Diorite results from the [[partial melting]] of a [[mafic]] rock above a [[subduction zone]]. It is commonly produced in [[volcanic arc]]s, and in cordilleran [[orogeny|mountain building]], such as in the [[Andes Mountains]], as large [[batholith]]s. The [[Extrusive (geology)|extrusive]] [[volcanic]] equivalent rock type is [[andesite]].

Revision as of 16:37, 12 July 2015

Diorite
Diorite classification on QAPF diagram
Mineral assemblage of igneous rocks

Diorite (/ˈdərˌt/ or /ˈd[invalid input: 'ɵ']ˌrt/) is a grey to dark-grey intermediate intrusive igneous rock composed principally of the minerals plagioclase feldspar (typically andesine), biotite, hornblende, and/or pyroxene. It is distinguished from gabbro on the basis of the composition of the plagioclase species, where average anorthite content of plagioclase in a diorite is less than 50 per cent. It may contain small amounts of quartz, microcline, and olivine. Zircon, apatite, titanite, magnetite, ilmenite, and sulfides occur as accessory minerals.[1] It can also be black or bluish-grey, and frequently has a greenish cast. 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. Diorite has a medium grain size texture and is occasionally porphyritic.

The phaneritic speckled texture common to diorite is due to random distribution of medium-sized grains of the white albite and black or nearly black color amphibole and pyroxene crystals, with minor glints of biotite. The common silicate mineral assemblage mainly includes sodium-rich plagioclase, calcium-rich plagioclase, amphibole, pyroxene, and biotite. Minor amounts of muscovite and quartz, and oxides, such as magnetite and ilmenite, may also be present. A dioritic rock containing feldspathoid mineral/s while absent of quartz is termed foid-bearing or foid diorite according to content. Diorite may also be porphyritic. Orbicular diorite shows alternating concentric growth bands of plagioclase and amphibole surrounding a nucleus within a diorite porphyry matrix.

Diorites may be associated with either granite or gabbro intrusions, into which they may subtly merge. Diorite results from the 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.

Occurrence

Diorite

Diorite is a relatively rare rock; source localities include Leicestershire (one name for microdiorite—markfieldite—exists due to the rock's being found in the village of Markfield) and Aberdeenshire, UK; Guernsey; Sondrio, Italy; Thuringia and Saxony in Germany; Finland; Romania; Northeastern Turkey; central Sweden; the Darrans range of New Zealand; the Andes Mountains; Basin and Range province; Minnesota in the USA, and Idahet in Egypt.

An orbicular variety found in Corsica is called corsite.

Historic use

Diorite is an extremely hard rock, making it difficult to carve grand work with. It is so hard that ancient civilizations (such as Ancient Egypt) used diorite balls to work granite. Its hardness, however, also allows it to be worked finely and take a high polish, and to provide a durable finished work.

One comparatively frequent use of diorite was for inscription, as it is easier to carve in relief than in three-dimensional statuary. Perhaps the most famous diorite work extant is the Code of Hammurabi, inscribed upon a 2.23 m (7 ft 4 in) pillar of black diorite. The original can be seen today in Paris' Musée du Louvre.[2] The use of diorite in art was most important among very early Middle Eastern civilizations such as Ancient Egypt, Babylonia, Assyria, and Sumer. It was so valued in early times that the first great Mesopotamian empire—the Empire of Sargon of Akkad—listed the taking of diorite as a purpose of military expeditions.

Although one can find diorite art from later periods, it became more popular as a structural stone and was frequently used as pavement due to its durability. Diorite was used by both the Inca and Mayan civilizations, but mostly for fortress walls, weaponry, etc. It was especially popular with medieval Islamic builders. In later times, diorite was commonly used as cobblestone; today many diorite cobblestone streets can be found in England, Guernsey and Scotland, and scattered throughout the world in such places as Ecuador and China. Although diorite is rough-textured in nature, its ability to take a polish can be seen in the diorite steps of St. Paul's Cathedral, London, where centuries of foot traffic have polished the steps to a sheen.

See also

References

  1. ^ Blatt, Harvey and Robert J. Tracy (1996) Petrology, W. H. Freeman, 2nd edition, p. 53 ISBN 0-7167-2438-3
  2. ^ The Louvre: Law Code of Hammurabi

External links