A beryl from Mewar (Rajasthan) shows two zones; the outer yellowish green border zone and the inner yellow core. The refractive index and cell dimensions of beryl increase from the core to the border. This increase seems to be due to the slightly higher FeO + Fe2O3 content of the border. It is proposed that the zoning is due to the isomorphous solid solution series between Al beryl and Fe beryl.
A study of zoned beryl from Rajasthan