Samarium

In nature, samarium is found in the Earth's crust, 6.47-7.0 ppm, in minerals such as monazite, bastnaesite, samarskite, cerite, orthite, ytterbite and fluorspar, of which the first two are the commercially important sources [5]. The isotopes found in nature are ¹⁴⁴Sm (3.1 %, stable), ¹⁴⁷Sm (15.0 %, T_½ = 1.06 · 10¹¹ years), ¹⁴⁸Sm (11.3 %, T_½ = 7 · 10¹⁵ years), ¹⁴⁹Sm (13.8 %, stable), ¹⁵⁰Sm (7.7 %, stable), ¹⁵²Sm (26.7 %, stable) and ¹⁵⁴Sm (22.7 %, stable) [5].

In pure solid form, samarium exist in the following forms:
α-form: rhombohedral crystal at < 917 °C [5]
β-form: body-centered cubic crystal at > 917 °C [5]