Abstract
Corrensite occurs as alteration products in basic to intermediate volcanic and pyroclastic rocks. Chlorite and saponite also widely occur in the similar rocks. This paper proves that refractive indices and birefringence are effective for the discrimination among those minerals. Chlorite shows lower birefringence and higher refractive indices than corrensite. On the other hand, saponite shows higher interference color and low refractive indices. Corrensite has hybrid properties of the two end members forming the interstratification. Namely, birefringence of corrensite is in the range of 0.01 to 0.03 and it is lower than that of saponite and higher than that of chlorite.
