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a pseudomorph of amphibole after pyroxene in magmatic rocks. The name of the pseudomorph derives from the Ural Region. Originally, the name was used for amphibole crystals having a pyroxene habit; later, it was applied to the fibrous aggregates produced upon the replacement of monoclinic pyroxenes by a blue-green amphibole. The mineralogical nature of this amphibole cannot be precisely determined by ordinary microscopic examination; usually it is actinolite, but in some cases it is hornblende containing as much as 5–6 percent Al2O3. Upon the uralitization of pyroxenes, the plagioclase either retains its luster or undergoes albitization. Uralitization is caused by the action of residual hydrothermal solutions; it is sometimes linked to subsequent metamorphism.