Yellow metal that tarnishes in contact with air .
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 . The isotopes found in nature are 144Sm (3.1 %, stable), 147Sm (15.0 %, T½ = 1.06 · 1011 years), 148Sm (11.3 %, T½ = 7 · 1015 years), 149Sm (13.8 %, stable), 150Sm (7.7 %, stable), 152Sm (26.7 %, stable) and 154Sm (22.7 %, stable) .
In pure solid form, samarium exist in the following forms:
α-form: rhombohedral crystal at < 917 °C 
β-form: body-centered cubic crystal at > 917 °C