Calcium sulfide is a chemical compound with the formula CaS. It consists of one calcium atom and one sulfur atom. This compound is typically found as a white or yellowish solid and is known for its ability to glow in the dark when exposed to certain types of light, a property that makes it useful in various applications, including phosphorescent materials. In industry, calcium sulfide is used in the production of sulfur and as a reducing agent in chemical reactions. It can also be employed in the manufacture of pigments and in the treatment of wastewater. Additionally, it plays a role in the extraction of metals from their ores.