Abstract
The existing Michel-Levy's interference color chart represents the retardation (interference color) only up to 2,500 mμm and fourth-order colors on A6 paper size. However, an interference color chart using a logarithmic plot (Fig. 1) represents retardation from l00 to 12,500 mμm and up to 24th-order colors on the same paper size.
Fig. 1 facilitates the accurate measurement of grain retardation. Such measurements, if followed by accurate measurement of grain thickness, permit the birefringence to be accurately calculated [Eq. (1)]. Fig. l permits quick, graphic solutions of Eq. (1) in the area from low-order to high-order colors.
ln case of idiomorphic orthopyroxene, estimation of maximum birefringence (γ-α) will be possible. The range of the retardation of fine-sand size orthopyroxene is from 2,500 to 5,000 mμm. Fig.1 only permits measurement of this high-order retardation and estimation of birefringence.
