The coral used as gem material is a branching skeleton like structure built by small marine animals. When polished it has a vitreous luster. It is used for necklaces and bracelets, for cabochons, ornamental objects and sculptures. It has a Mohs' hardness of 3 - 4 which means it is fairly soft when compared to material such as Amethyst, which has a Mohs' hardness of 7.