A Trial for the Rapid Determination of Volcanic Rocks: The relation of the refractive indices of melted rock-glasses to their chemical compositions

It becomes evident that the refractive indices of artificially prepared rock-glasses easily by melting in the flame of oxygen-gas have an intimate relation to their chemical compositions, being clearly shown on certain smooth curves. As to some of the Tertiary calc-alkalic rocks obtained from the San-in district, is their interrelation inspected practically in the present paper. The method hereunder referred to may be utilizable to determine rapidly a large number of volcanic rocks such as tuffs or tuff-breccias.