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amphibole

amphibole (ăm´fəbōl´), any of a group of widely distributed rock-forming minerals, magnesium-iron silicates, often with traces of calcium, aluminum, sodium, titanium, and other elements. The amphibole minerals are closely related in crystal structure, but they crystallize in two different systems, orthorhombic and monoclinic; their close structural relationship is reflected in uniform prism angles of about 56° and 124° and in good cleavages parallel to these prisms. They are commonly green to black, but may be colorless, white, yellow, blue, or brown. The amphibole minerals are found both in igneous and metamorphic rocks. The commonest form is hornblende; other species include anthophyllite, cummingtonite, tremolite, actinolite, riebeckite, and glaucophane. A variety of jade, called nephrite, consists of actinolite in a finely fibrous form.

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amphibole

amphibole Any of a large group of complex rock-forming minerals characterized by a double-chain silicate structure (Si4O11). They all contain water as OH ions and usually calcium, magnesium, iron. Found in igneous and metamorphic rocks, they form wedge-shaped fragments on cleavage. Crystals are orthorhombic or monoclinic.

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