Relations between barium content and the physical and optical properties in the manganoan phlogopite-kinoshitalite series

Abstract

Manganobarian phlogopite and kinoshitalite, a barium brittle mica, from the Noda-Tamagawa mine, Northeast Japan, have an apparent solid solution series with a wide range of Ba content. The Ba content varies from 5.3 atomic percent to 55.6 atomic percent in the Na–K–Ca–Ba system.Physical and optical properties change with the increase of Ba content in the manganoan phlogopite-kinoshitalite series : Specific gravity increases linearly. Birefringence decreases rapidly between 20.7 percent and 34.2 percent Ba, as the result of the increase of α.Specimens containing as much as 34.2 percent Ba are brittle with smoother cleavage flakes and have lower birefringence (0.020) than manganoan phlogopite. Therefore manganoan phlogopite is thought to change into kinoshitalite at a composition near Ba:K=1:2.