HgS

HgS, mercury sulfide, is an inorganic compound that occurs naturally mainly as the mineral cinnabar, the red form of the compound and the principal ore of mercury. The compound has two polymorphs: red cinnabar (alpha-HgS) and metacinnabar (beta-HgS), with cinnabar being the stable phase at ordinary conditions.

Natural occurrence and structure: Cinnabar forms in hydrothermal veins and hot-spring deposits and has been mined for centuries. It is found in various regions around the world, including historic and current mercury-producing districts in Spain, Slovenia, Mexico, Peru, and China.

Properties: HgS is highly insoluble in water and is relatively stable at ambient conditions. It decomposes or releases mercury if heated strongly. The mineral is prized for its vivid red color; the pigment vermilion is a historical use of synthetic or natural HgS. In material science, HgS has been studied for its semiconducting and optical properties, though its toxicity limits widespread use.

Uses and hazards: Historically, cinnabar was processed to extract mercury and used as the red pigment vermilion in art and decoration. Today the use of mercury sulfide is much restricted due to the toxicity of mercury compounds. Handling and processing require strict safety measures to prevent inhalation or ingestion of mercury-containing dust or vapors, and environmental releases are a concern.

Summary: HgS is the red mineral cinnabar and the main natural source of mercury. It exists in multiple forms, is insoluble in water, and has important historical significance as a pigment and ore, but its use is limited by mercury’s toxicity.