Color in feldspars

Pure feldspar, free of exsolution, is colorless. However, minor chemical substituents, inclusions, interference effects from exsolution lamellae, and radiation damage can produce color in the mineral. Chemical impurities produce the yellow color of sanidine, orthoclase and calcic plagioclase, the blue to green colors of amazonite, and the blue-green color of sodic plagioclase. Inclusions create a wide variety of colors: pink, brick-red, and grays are common; orange, tan and green may also occur. Aventurine and shiller effects also result from inclusions. Radiation produces gray or smoky colors. Exsolution phenomena and oriented intergrowths produce interference colors, schiller and chatoyancy. This chapter describes the colored varieties of feldspar and their absorption spectra and coloration mechanisms. Labradorescence and moonstone effects, which are produced by interference phenomena and scattering phenomena, were discussed in Chapter 10