Ag2S

Silver sulfide, with the chemical formula Ag2S, is a binary compound of silver and sulfur. In nature it occurs as the mineral argentite and as the low-temperature monoclinic phase acanthite. Acanthite is typically the stable form at room temperature, while argentite is the high-temperature cubic polymorph; upon cooling the cubic phase can persist only metastably in some samples.

Ag2S exists in two polymorphs: the monoclinic acanthite (low-temperature form) and the cubic argentite (high-temperature form). The material undergoes a phase transition between these forms with changes in temperature, which affects its structural and physical properties.

Physically, Ag2S is a soft, dark solid with a metallic luster and a relatively high density for a sulfide, commonly cited around 7 g/cm3. It is generally insoluble in water and is sensitive to acids, which can release hydrogen sulfide gas. In air, silver sulfide can form tarnish on silver-containing materials. As a semiconductor, Ag2S has attracted interest for fundamental studies and potential applications in electronics and photoelectrochemical devices.

Occurrence and geology: As a natural mineral, Ag2S forms in hydrothermal and ore-deposit environments, often associated with native silver and other sulfide minerals. Its presence can indicate sulfidic conditions during ore formation.

Synthesis and uses: In the laboratory, Ag2S can be prepared by combining silver ions with sulfide sources to precipitate the compound. It is studied for its semiconductor properties and potential applications in electronic, optoelectronic, and catalytic contexts, though practical use is limited by stability and handling considerations.

Safety: Handling should consider the potential release of toxic hydrogen sulfide upon acidifying the solid. Standard laboratory safety practices apply, including working in appropriate fume conditions and avoiding inhalation of any sulfur compounds.