Table 3.
Selected physical∕chemical properties for holmium, erbium, and thulium [Source: Nature’s Building Blocks: An A–Z Guide to the Elements (Ref. 17)].
| Property∕element | Holmium | Erbium | Thulium |
|---|---|---|---|
| Atomic number | 67 | 68 | 69 |
| Density | 8.80 g∕cm3 | 9.07 g∕cm3 | 9.32 g∕cm3 |
| Metallicity | Relatively soft and malleable | Soft and malleable | Soft, malleable, and ductile |
| Stability | Slowly attacked by oxygen | Slowly tarnishes in air | Slowly tarnishes in air |
| Slowly attacked by water | Very slowly reacts with water | Reacts with water | |
| Dissolves in dilute acids | Dissolves in acids | Dissolves in dilute acids | |
| Abundance (in Earth’s crust) | 1.4 ppm | 4 ppm | 0.5 ppm |