Determination of 2V angle in plagioclase by the analytical method using φ values multiple of 90º

Abstract

The 2V angle of plagioclases is determined through a computer program by the analytical method of Chomard. Determinations involved 28 individuals of which seven with two repetitions. Twelve different extinction operations were used as a result of the combinations: φ= 0º, φ= 90º, φ= 180º, φ= 270º and Θ = 15º, Θ = 30º, Θ = 45º. For the extinction operations used the application of the analytical method to plagioclases should be avoided.