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ultrabasic

[uhl-truh-bey-sik] /ˌʌl trəˈbeɪ sɪk/
adjective
1.
(of rocks) containing iron and magnesium, with little or no silica.
Also, ultramafic.
Origin
1890-1895
1890-95; ultra- + basic
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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British Dictionary definitions for ultra-basic

ultrabasic

/ˌʌltrəˈbeɪsɪk/
adjective
1.
(of such igneous rocks as peridotite) containing less than 45 per cent silica
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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ultra-basic in Science
ultrabasic
  (ŭl'trə-bā'sĭk)   
Containing magnesium and iron and only a very small amount of silica. Used of igneous rock, and often used interchangeably with ultramafic. Peridotite is an ultrabasic rock.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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