gems, Ceylon, Sri Lanka, spinel, refractive index

Körnke reports precise measurements of the refractive index and dispersion of a blue-violet spinel from Ceylon, undertaken to expand the available optical data for gem spinels. Using the minimum-deviation method, he measured refractive indices over wavelengths from 762.8 to 420.0 nm. The refractive index increases from 1.70893 at 762.8 nm to 1.73332 at 420.0 nm, and the results are presented both as a table and a dispersion curve. Körnke notes that the measurements agree almost exactly with values previously obtained by K. Schlossmacher for another blue-violet spinel.