Optical characters, particularly optic dispersion, of sodic- and subcalcic-amphiboles in Sanbagawa schists

Abstract

Na and Na-Ca amphiboles often show anomaly of optical extinction. The dependence of 2V_X and extinction angle on the wavelength of light (Cd, Na, and Hg lamps) has been measured and described along with the chemical composition of amphiboles. The maximum angle of extinction is 43° and the values of 20 to 40° is common in amphiboles of quartz schists in the garnet and albite-biotite zones of the Sanbagawa metamorphic belt.