Containing magnesium and iron and only a very small amount of silica. Used of igneous rock. (adjective)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "ultrabasic" in a sentence
"The higher elevations of the Nicobars often contain serpentine and gabbro formations, whereas at lower elevations Eocene sediments (sandstones, shales, and siltstones) with ultrabasic igneous intrusions predominate."
"Metamorphic schist, limestone, ultrabasic rocks, and volcanic rocks are the main parent rock formations of the ecoregion."
"This ecoregion also contains patches of ultrabasic rocks."