Basanite

Basanite

Basanite (pronEng|ˈbæsənaɪt) is an igneous, volcanic (extrusive) rock with aphanitic to porphyritic texture. The mineral assembly is usually abundant feldspathoids (nepheline or leucite), plagioclase, and augite, together with olivine and lesser iron-titanium oxides such as ilmenite and magnetite-ulvospinel; minor alkali feldspar may be present, as illustrated by the position of the field for basanite in the QAPF diagram. Clinopyroxene (augite) and olivine are common as phenocrysts and in the matrix. The augite contains significantly greater titanium, aluminium and sodium than that in typical tholeiitic basalt. Quartz is absent, as are orthopyroxene and pigeonite. Chemically, basanites are low in silica (42 to 45% SiO2) and high in alkalis (3 to 5.5% Na2O and K2O) compared to basalt, which typically contains more SiO2, as evident on the diagram used for TAS classification. Nephelinite is yet richer in Na2O plus K2O compared to SiO2.

Basanites occur both on continents and on ocean islands. For example, together with basalts, they are produced by hotspot volcanism in the Hawaiian and the Comores Islands. (e.g., [http://gsa.confex.com/gsa/2003AM/finalprogram/abstract_65599.htm] )

The term "basanite" has been used occasionally to refer to the mineral jasper, for example a black flinty or cherty jasper found in several New England states of the U. S. A. Such varieties of jasper are also informally known as Lydian stone, lydite and touchstone and have been used to test for the purity of precious metal alloys.

References

*Blatt, Harvey and Robert J. Tracy (1996) "Petrology", 2nd ed., W. H. Freeman ISBN 0-7167-2438-3
* [http://gsa.confex.com/gsa/2003AM/finalprogram/abstract_65599.htm Buchwaldt, Robert (2003) Geochemistry and Petrology of a Miocene Trachyte-Basanite Suite from Mt. Tsaratanana, Northern Madagascar, Abstract.]
* [http://www.mindat.org/min-9173.html Mindat data]


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  • Basanite — Bas a*nite, n. [L. basanites lapis, Gr. ba sanos the touchstone: cf. F. basanite.] (Min.) Lydian stone, or black jasper, a variety of siliceous or flinty slate, of a grayish or bluish black color. It is employed to test the purity of gold, the… …   The Collaborative International Dictionary of English

  • basanite — ● basanite nom féminin Basalte alcalin à fort déficit de silice, formé de plagioclase, d augite, d olivine et d un feldspathoïde …   Encyclopédie Universelle

  • Basanite — Basalte Structure géométrique typique des orgues basaltiques (Près du fleuve Skjálfandafljót, Islande) …   Wikipédia en Français

  • basanite — /bas euh nuyt , baz /, n. Petrog. a basaltic rock composed chiefly of plagioclase, olivine, and augite. [1745 55; < L basanites; see BASALT] * * * ▪ rock       extrusive igneous rock that contains calcium rich plagioclase feldspar (usually… …   Universalium

  • basanite — noun A basaltic extrusive rock, similar to chert Syn: lydite …   Wiktionary

  • basanite — bas·a·nite …   English syllables

  • basanite — ˈbasəˌnīt, azə noun ( s) Etymology: Latin basanites more at basalt 1. : touchstone 1 2. : an extrusive igneous rock composed of plagioclase, augite, olivine …   Useful english dictionary

  • Basanite — noun see touchstone I …   Useful english dictionary

  • Basaltes — Basalte Structure géométrique typique des orgues basaltiques (Près du fleuve Skjálfandafljót, Islande) …   Wikipédia en Français

  • Basaltique — Basalte Structure géométrique typique des orgues basaltiques (Près du fleuve Skjálfandafljót, Islande) …   Wikipédia en Français

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