Definition of "ultramafic" [ultramafic]

• Ultrabasic. (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.

• "That was as far as the analysis went in the past, but much newer work in mineral physics - specifically concerning what are known as "ultramafic" rocks - have changed all that."
• "The second and third types of vent sites are hosted in rocks called ultramafic that form deep below the seafloor and are composed of material similar to the much hotter lavas that erupted on Earth's very earliest seafloor, thousands of millions of years ago."
• "Geological Survey have surveyed the United States and found 6,000 square miles (15,500 square kilometers) of so-called ultramafic rocks at or near the surface that could be ideal for storing the excess gas."