(of rocks) containing iron and magnesium, with little or no silica.
Origin of ultrabasic
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Historical Examples of ultrabasic
These range from acid to ultrabasic types and include granite, augite-diorite, picrite and serpentine.
(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
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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