anorthosite


anorthosite
anorthositic /an aw'theuh sit"ik/, adj.
/an awr"theuh suyt'/, n. Petrol.
a granular plutonic rock composed largely of labradorite or a more calcic feldspar.
[1860-65; < F anorthose anorthoclase (an- AN-1 + Gk orthós straight) + -ITE1]

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Type of igneous rock composed predominantly of calcium-rich feldspar.

It is considerably less abundant than either basalt or granite, but the complexes in which it occurs are often immense. All anorthosites found on the earth consist of coarse crystals, but some from the moon are finely crystalline.

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rock
      type of intrusive igneous rock composed predominantly of calcium-rich plagioclase feldspar. All anorthosites found on Earth consist of coarse crystals, but some samples of the rock taken from the Moon are finely crystalline. Most anorthosites formed during Precambrian times.

      Anorthosite is considerably less abundant than either basalt or granite, but the complexes in which it occurs are, nevertheless, often of immense size. For instance, about 155,000 square km (60,000 square miles) of eastern Canada is underlain by anorthosite, the Saguenay Mass alone accounting for a tenth of this. The Morin Anorthosite in the same area occupies 2,600 square km (1,040 square miles), and the Adirondack Anorthosite is exposed over an area of about 3,900 square km (1,560 square miles). The Bushveld Complex underlies an area of about 50,000 square km (20,000 square miles); and the Great Dyke of Zimbabwe, another layered complex, has been traced for more than 480 km (300 miles). Anorthosite is also found on the lunar surface.

      Although these large masses are generally supposed to provide the best sample of the deep lithosphere (the outer shell of the Earth), they often appear to be floored over most of their outcrop area. They usually occur as laccoliths (low domelike intrusions with a flat base found between sedimentary beds), lopoliths (laccoliths with basin-shaped bases), or sills (tabular intrusions between other rocks). The Canadian anorthosites are thought to be laccolithic, while the Adirondack Anorthosite is considered a floored sheet. The thickness of the Sudbury Lopolith is estimated at 3 km (1.9 miles), that of the Bushveld at 5 km (3 miles). Anorthosite dikes (slablike, steeply inclined intrusions along fissures) are very rare, and effusive equivalents of anorthosite are unknown.

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Universalium. 2010.

Look at other dictionaries:

  • Anorthosite — (pronEng|æˈnɔrθəsaɪt/, /ə ) is a phaneritic, intrusive igneous rock characterized by a predominance of plagioclase feldspar (90–100%), and a minimal mafic component (0–10%). Pyroxene, ilmenite, magnetite, and olivine are the mafic minerals most… …   Wikipedia

  • Anorthosite — lunaire, Musée national d histoire naturelle, Washington, DC. L Anorthosite est une roche phanéritique intrusive et ignée, composée pour la plus grande partie de feldspath plagioclase (90 100%), et d une petite quantité (0 10%) de composants… …   Wikipédia en Français

  • anorthosite — ● anorthosite nom féminin Roche plutonique presque entièrement constituée de plagioclases. ● anorthosite (synonymes) nom féminin Roche plutonique presque entièrement constituée de plagioclases. Synonymes : plagioclasite …   Encyclopédie Universelle

  • Anorthosite — A*nor tho*site, n. [F. anorthose triclinic feldspar (fr. Gr. ? priv. + ? straight) + ite.] (Petrol.) A granular igneous rock composed almost exclusively of a soda lime feldspar, usually labradorite. [Webster 1913 Suppl.] || …   The Collaborative International Dictionary of English

  • anorthosite — [an ôr′thō sīt΄; an ôr′thəsīt΄] n. [< Fr anorthose < Gr an , not + orthos (see ANORTHITE) + ITE1] a type of gabbro, usually light colored, made up almost entirely of plagioclase feldspars, esp. labradorite …   English World dictionary

  • anorthosite — noun A phaneritic, intrusive igneous rock characterized by a predominance of plagioclase feldspar. The second, or Labrador series is characterized, as already remarked, by the predominance of great beds of anorthosite, composed chiefly of… …   Wiktionary

  • anorthosite — noun Etymology: French anorthose, a feldspar, from a + Greek orthos more at orth Date: 1863 a granular plutonic igneous rock composed almost exclusively of a soda lime feldspar (as labradorite) • anorthositic adjective …   New Collegiate Dictionary

  • anorthosite — [ə nɔ:θəsʌɪt] noun Geology a granular igneous rock composed largely of labradorite or another plagioclase. Origin C19: from Fr. anorthose plagioclase + ite1 …   English new terms dictionary

  • anorthosite — an·or·tho·site …   English syllables

  • anorthosite — an•or•tho•site [[t]ænˈɔr θəˌsaɪt[/t]] n. pet a granular plutonic rock composed largely of labradorite or a more calcic feldspar • Etymology: 1860–65; < F anorthose (an I+ Gk orthós straight) + ite I an•or tho•sit′ic ˈsɪt ɪk adj …   From formal English to slang


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