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(named after H. B. Saussure), a fine-grained aggregate of the minerals zoisite and albite, sometimes also containing calcite and sericite impurities or, less often, chlorite. Saussurite is produced by the alteration of plagioclases containing a small amount of anorthite. Particles range in size from thousandths to hundredths of a millimeter and can be distinguished only under a microscope. Most commonly, saussurite replaces plagioclases having an andesine-labradorite composition. It is formed during the metamorphosis of rocks, and is encountered most frequently in gabbros, diabases, and dolerites. The process by which plagioclases are replaced by saussurite is called saussuritization.