basalt

[buh-sawlt, bas-awlt, bey-sawlt]
noun
the dark, dense igneous rock of a lava flow or minor intrusion, composed essentially of labradorite and pyroxene and often displaying a columnar structure.

Origin:
1595–1605; < Latin basaltēs, a misreading, in manuscripts of Pliny, of basanītēs < Greek basanī́tēs (líthos) touchstone, equivalent to básan(os) touchstone (ultimately < Egyptian bh̬n(w) graywacke) + -ītēs -ite1

basaltic, basaltine [buh-sawl-tin, -tahyn] , adjective
subbasaltic, adjective
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Based on the Random House Dictionary, © Random House, Inc. 2014.
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Collins
World English Dictionary
basalt (ˈbæsɔːlt)
 
n
1.  See flood basalt a fine-grained dark basic igneous rock consisting of plagioclase feldspar, a pyroxene, and olivine: the most common volcanic rock and usually extrusive
2.  a form of black unglazed pottery resembling basalt
 
[C18: from Late Latin basaltēs, variant of basanītēs, from Greek basanitēs touchstone, from basanos, of Egyptian origin]
 
ba'saltic
 
adj

Collins English Dictionary - Complete & Unabridged 10th Edition
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Etymonline
Word Origin & History

basalt
c.1600, from L.L. basaltes, misspelling of L. basanites "very hard stone," from Gk. basanites "a species of slate used to test gold," from basanos "touchstone." Not connected with salt. Said by Pliny ["Historia," 36.58] to be an African word, perhaps Egyptian bauhan "slate." Any hard, very dark rock
would do as a touchstone; the assayer compared the streak left by the alleged gold with that of real gold or baser metals. Hence Gk. basanizein "to be put to the test, examined closely, cross-examined, to be put to torture."
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
basalt   (bə-sôlt', bā'sôlt')  Pronunciation Key 
A dark, fine-grained, igneous rock consisting mostly of plagioclase feldspar and pyroxene, and sometimes olivine. Basalt makes up most of the ocean floor and is the most common type of lava. It sometimes cools into characteristic hexagonal columns, as in the Giant's Causeway in Anterim, Northern Island. It is the fine-grained equivalent of gabbro.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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American Heritage
Cultural Dictionary
basalt [(buh-sawlt, bay-sawlt)]

A hard, dense igneous rock that makes up much of the material in tectonic plates. The part of the Earth's crust beneath the oceans consists mainly of basalt whereas continental crust consists mainly of less dense rocks, such as granite. (See plate tectonics.)

The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Example sentences
The surging water washed away the basalt and much of the rich topsoil.
But under the water, volcanoes continued to erupt, sending up magma and forming
  mountains of basalt.
Craters dot the surface of a lunar mare, or basalt sea, on the dark side of the
  moon.
Scientists have looked for evidence of life in rocks before but only on the
  surface of basalt rocks or in sedimentary layers.
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