Silver(I) sulfide

Silver(I) sulfide, also known as silver sulfide and silver sulphide, is a chemical compound. Its chemical formula is Ag2S. It contains silver in its +1 oxidation state. It also contains sulfide ions.
Properties.
It is a black solid. It reacts with acids. It is heavy. It can irritate the skin.
Occurrence and preparation.
It exists in the ground as acanthite and argentite. It is also made when silver is in air containing hydrogen sulfide. The oxygen in air cannot oxidize the silver directly; the hydrogen sulfide helps it. It is the tarnish on silver items.
Uses.
It is mostly an unwanted product when silver tarnishes.