1. relating to or denoting igneous rocks that are very low in silica and rich in magnesium and iron
Usage: geology

Examples

• The ultramafic rocks in the Earth’s mantle contain high concentrations of olivine.
• Geologists discovered ultramafic intrusions in the mountain range.
• The ultramafic composition indicates the rock formed deep within the Earth.
• Serpentine is a common mineral found in ultramafic rocks.
• The ultramafic layer provides clues about the planet’s interior structure.