Holmium(III) Oxide, or Holmium Oxide is a highly insoluble thermally stable Holmium source. It is a chemical compound of a rare-earth element holmium and oxygen with the formula Ho2O3. Holmium oxide occurs in small quantities in the minerals monazite, gadolinite, and in other rare-earth minerals. Holmium metal easily oxidizes in air; therefore presence of holmium in nature is synonymous with that of holmium oxide. It is suitable for glass, optic and ceramic applications.