Ultramafic Rock
Ultramafic (also referred to as ultrabasic) rocks are igneous and meta-igneous rocks with very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are composed of usually greater than 90% mafic minerals (dark colored, high magnesium and iron content). The Earth's mantle is composed of ultramafic rocks.
Read more about Ultramafic Rock: Intrusive Ultramafic Rocks, Volcanic Ultramafic Rocks, Ultrapotassic Ultramafic Rocks, Metamorphic Ultramafic Rocks, Distribution in Space and Time, Soil and Regolith Developed On Ultramafic Rock
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—Thomas Szasz (b. 1920)