| Tb/TREM (% min.) | 99.99 | 99.99 | 99.9 | 99 |
| TREM (% min.) | 99.9 | 99.5 | 99 | 99 |
| Rare Earth Impurities | ppm max. | ppm max. | % max. | % max. |
| Eu/TREM Gd/TREM Dy/TREM Ho/TREM Er/TREM Tm/TREM Yb/TREM Lu/TREM Y/TREM | 10 20 30 10 10 10 10 10 10 | 10 20 50 10 10 10 10 10 10 | 0.03 0.03 0.05 0.03 0.03 0.005 0.005 0.005 0.01 | 0.01 0.5 0.3 0.05 0.03 0.01 0.01 0.01 0.03 |
| Non-Rare Earth Impurities | ppm max. | ppm max. | % max. | % max. |
| Fe Si Ca Al Mg W Ta O C Cl | 200 100 200 100 100 100 50 300 100 50 | 500 100 200 100 100 100 100 500 100 50 | 0.15 0.01 0.1 0.05 0.05 0.1 0.01 0.2 0.01 0.01 | 0.2 0.02 0.2 0.1 0.1 0.2 0.05 0.25 0.03 0.02 |