Erbium

In nature, erbium is found in the Earth's crust, 2.47-3.5 ppm, in minerals such as xenotime, fergusonite, gadolinite, euxenite, polycrase and blomstrandine [4]. The isotopes found in nature are ¹⁶²Er (0.14 %, stable), ¹⁶⁴Er (1.61 %, stable), ¹⁶⁶Er (33.6 %, stable), ¹⁶⁷Er (22.95 %, stable), ¹⁶⁸Er (26.8 %, stable) and ¹⁷⁰Er (14.9 %, stable) [4].