• synonyms


  1. (of rocks) containing iron and magnesium, with little or no silica.
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Origin of ultrabasic

First recorded in 1890–95; ultra- + basic
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for ultrabasic

Historical Examples

  • These range from acid to ultrabasic types and include granite, augite-diorite, picrite and serpentine.

    Encyclopaedia Britannica, 11th Edition, Volume 8, Slice 8


British Dictionary definitions for ultrabasic


  1. (of such igneous rocks as peridotite) containing less than 45 per cent silica
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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

ultrabasic in Science


  1. 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.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.