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adamellite A rock of granitic composition (see GRANITE) characterized by the presence of quartz, plagioclase feldspar, and potassic feldspar (see ALKALI FELDSPAR) accompanied by biotite and/or hornblende. The two feldspar types occur in approximately equal proportions, the plagioclase composition lying within the oligoclase range. The name is derived from the type locality of Adamello in the Tyrol where granites of this type were originally defined. In Britain the best-known example occurs at Shap Fell in Cumbria.