 The most stable oxide of samarium is the sesquioxide Sm2O3 . As many other samarium compounds , it exists in several crystalline phases . The trigonal form is obtained by slow cooling from the melt . The melting point of Sm2O3 is rather high ( 2345 ° C ) and therefore melting is usually achieved not by direct heating , but with induction heating , through a radio @-@ frequency coil . The Sm2O3 crystals of monoclinic symmetry can be grown by the flame fusion method ( Verneuil process ) from the Sm2O3 powder , that yields cylindrical <unk> up to several centimeters long and about one centimeter in diameter . The <unk> are transparent when pure and defect @-@ free and are orange otherwise . Heating the metastable trigonal Sm2O3 to 1900 ° C converts it to the more stable monoclinic phase . Cubic Sm2O3 has also been described . 
