\rē-▐al-▐gär, -gәr\ n [ME, fr. ML, fr. Catalan, fr. Arabic rahj al-ghār powder of the mine] (15c) As2S2. Arsenic disulfide mineral, which was used as a pigment under the name, “arsenic orange.” Its chemical and physical properties are similar to those of orpiment. In modern times, it is not used as a pigment because of its toxicity.