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cummingtonite(kŭm`ĭngtənīt): see amphiboleamphibole
, any of a group of widely distributed rock-forming minerals, magnesium-iron silicates, often with traces of calcium, aluminum, sodium, titanium, and other elements.
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a mineral from the series of monoclinic amphiboles. The chemical composition is (Mg, Fe)7[Si4O11]2 (OH)2; admixtures of Ca, Al, Mn, and Na are common. The Mg-rich members are called cupfferite; the more ferruginous ones are called griinerite. Cummingtonite forms fibrous aggregates or radiating, columnar masses of brownish gray to dark brown color. It has a hardness of 5.5–6 on the mineralogical scale; its density ranges from 3,100 to 3,600 kg/m3. Cummingtonite is a characteristic mineral of metamorphic schists. It is also encountered in contact-metasomatic skarns and metamorphogenetic ore deposits.