Antimony(III) sulfide occurs in two modifications: The orange-red, amorphous form is not stable. When heated in the absence of oxygen, the dark grey, crystalline form is obtained. When heated vigorously in air or in an oxygen stream, antimony(III) sulfide oxidizes to antimony(III) oxide and sulfur dioxide. In boiling water or with water vapor it slowly decomposes to antimony(III) oxide and hydrogen sulfide. Explosive reactions may occur with oxidizing agents such as potassium chlorate or silver oxide.
When separating the mineral stibnite from the bedrock, only an impure product is obtained. The stibnite is first heated to about 550 °C so that the low-melting antimony sulfide flows out in pure form. This up to 98 percent pure antimony sulfide is marketed as dark grey antimonium crudum. The orange-red modification is obtained by introducing hydrogen sulfide into an acidic, aqueous antimony(III) chloride solution. The fusion of the elements antimony and sulfur also produces antimony(III) sulfide.
Antimony(III) sulphide is contained in the match heads together with potassium chlorate. When rubbing against the friction surface, which consists of red phosphorus, there is a small jet of flame which ignites the match. Antimony(III) sulfide is also found as an additive in fireworks. As a light-sensitive semiconductor it is used in optoelectronic devices.
Antimony black was a historical pigment extracted from the mineral stibnite: Already the Egyptian women used it to make black eye make-up. Due to its bactericidal effect, it was used in ancient times in creams to treat wounds and ulcers. Paracelsus later even used it for internal treatment. Due to its toxicity it is no longer used for medical or cosmetic purposes.
Repeated inhalation of dust can cause chronic diseases of the lungs or cardiovascular system. Results from animal experiments with antimony(III) sulphide suggest that antimony(III) sulphide could also be carcinogenic for humans.