ultrabasic

[uhl-truh-bey-sik]

adjective

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

Also ultramafic.

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 of ultrabasic

These range from acid to ultrabasic types and include granite, augite-diorite, picrite and serpentine.
Encyclopaedia Britannica, 11th Edition, Volume 8, Slice 8
Various

British Dictionary definitions for ultrabasic

ultrabasic

adjective

(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

ultrabasic 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.