Gadolinite-(Y): Gemstone Information
Gadolinite-(Y) is Y2Fe2Be2Si2O10 and usually occurs in very dark green to black metamict (originally monoclinic) masses from which the occasional large cabochon has been fashioned. The hardness is 6.5–7 and the SG 4.41. The RI for the alpha and gamma rays is 1.77–1.78 and 1.78–1.82 (no data for the beta ray), biaxial positive though isotropic when metamict. Any birefringence will be in the range 0.01–0.04. Gadolinite-(Y) occurs in granite and alkalic granite pegmatites. Specimens occur at several locations in Norway and in Texas, USA.