Andesine is a silicate mineral, a member of the plagioclase feldspar solid solution series. Its chemical formula is (Ca, Na)(Al, Si)4O8, where the ratio of albite to anorthite (Na:Ca) is 50:50 to 70:30. The formula may be written as Na0.5-0.7Ca0.3-0.5Al1.3-1.5Si2.5-2.7O8. The plagioclase feldspars are a continuous solid solution series and as such the accurate identification of individual members requires detailed optical study, chemical analysis or density measurements. Refractive indices and specific gravity increase directly with calcium content. It is sometimes used as a gemstone.

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