Mercury(II) sulfide (HgS): properties, forms, uses, and safety

Physical and chemical characteristics

HgS shows two well known polymorphs: a red, trigonal form called cinnabar and a black, cubic form called metacinnabar. The red form is dense, has a distinctive deep red color and a crystal habit often forming granular or massive deposits. The compound is essentially insoluble in water and relatively stable in ordinary conditions, but it decomposes on strong heating, releasing toxic mercury vapors. For details on its ionic components see mercury ions and sulfide.

History, occurrence and extraction

Cinnabar has been mined for centuries as the main source of elemental mercury; historical miners roasted HgS to drive off sulfur and recover metallic mercury. It is typically found in hydrothermal veins and near volcanic regions where mercury-bearing fluids precipitate sulfide minerals. Geologists and chemists often note the mercury +2 state; further background is available at oxidation state references.

Uses and cultural significance

Beyond ore production, powdered red HgS was the basis for the pigment vermilion used in painting, decoration, and lacquerware across many cultures. It also appears in historical medicines and ritual practices, though such uses carried health risks. Modern applications are limited because of toxicity and the availability of safer pigments and reagents.

Key practical points include:

• Primary use historically: source of elemental mercury and pigment.
• Two major forms: red cinnabar (hexagonal/trigonal) and black metacinnabar (cubic).
• Low solubility but hazardous when heated or ingested due to mercury exposure.

Because of the health dangers associated with mercury, handling and disposal are strictly regulated in many jurisdictions. For authoritative safety and technical references consult further reading.