Reexamination of high-temperature optics of natural sodic plagioclases

Thirty three years ago, the present author described the high-temperature optics of natural sodic plagioclases in Miocene rhyolites from northern Japan. In this paper, the same specimens of sodic plagioclases are carefully reexamined with aids of EPMA to check and revise the author’s previous diagrams. Point-by-point chemical analyses followed by the measurement of extinction angles are practiced on some zoned plagioclases perpendicular to a-axis (PM). The results show that the optical data are still useful.