Transmission of Inidan Mica between 300 and 1,000 mµ and its Visual Classification

INDIA produces ruby and green muscovite mica. Depending on the â stainsâ and inclusions each is visually classified into a number of groups, namely, â clearâ , â good-stainedâ , â fair-stainedâ , â stainedâ , â heavily stainedâ , â densely stainedâ , â black-dottedâ , â black-spottedâ , etc. It has been reported^1,2 that any visual classification has little bearing on the electrical properties of mica. Little information is available on the transmission of natural mica in the region of 300â 1,000 mµ,. Popper³ has reported that the absorption in the ultra-violet region of the Congo green muscovite is more than that of the Rhodesian ruby and synthetic mica. Spectral absorption for Russian muscovite and phlogopite micas in the region of 220â 1,200 mµ was studied by Grum-Grzhimails et al.⁴ and Melankholin⁵. To our knowledge, no such investigation of the spectral transmission of Indian muscovite has yet been reported. This communication reports our investigations of the optical transmission of Indian muscovite and its correlation with the visual classification.