Ultrabasic Rock

an IGNEOUS ROCK that contains many silicate minerals of iron and magnesium such as AMPHIBOLES and PYROXENES, and with SILICA occurring as quartz.

Taken from Dictionary of Science

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An igneous rock with a very low silica content and rich in minerals such as hypersthene, augite and olivine. These rocks are also known as ultramafic rocks.

Taken from Geology.com