Indium(III) Sulfide is the inorganic compound with the formula In2S3. Three different structures ("polymorphs") are known: yellow, α-In2S3 has a defect cubic structure, red β-In2S3 has a defect spinel, tetragonal, structure, and γ-In2S3 has a layered structure. The red, β, form is considered to be the most stable form at room temperature, although the yellow form may be present depending on the method of production. Like related covalent solids, In2S3 is insoluble in all solvents. It is attacked by acids and by sulfide. It is slightly soluble in Na2S.Indium sulfide was the first indium compound ever described, being reported in 1863. Reich and Richter determined the existence of indium as a new element from the sulfide precipitate.