Stibnite
Stibnite in the Carnegie Museum of Natural History
General
Chemical formula	antimony sulfide (Sb2S3)
Identification
Color	Steel gray to dull gray. Black iridescent tarnish may be present
Crystal habit	Massive, radiating and elongated crystals. Massive and granular
Crystal system	Orthorhombic
Cleavage	Perfect
Fracture	Small-scale subconchoidal
Mohs Scale hardness	2
Luster	Splendent on fresh crystals surfaces, otherwise metallic
Refractive index	Opaque
Streak	Similar to color
Specific gravity	4.56 - 4.62
Solubility	decomposed with hydrochloric acid
Major varieties
Metastibnite	Earthy, reddish deposits

Stibnite, sometimes called antimonite, is a sulfide mineral with the formula Sb₂S₃. This soft grey material crystallizes in an orthorhombic space group. It is the most important source for the metaloid antimony.¹ The abbreviation for antimony, Sb, is taken from stibnite.

Formation, structure, reactivity

Sb₂S₃ forms when antimony(III) compounds are treated with hydrogen sulfide. This reaction gives a black precipitate:

2 Sb³⁺ + 3 H₂S → Sb₂S₃ + 6 H⁺

This reaction is reversed by hydrochloric acid.

Stibnite is attacked by potassium hydroxide solution and dissolves in solutions of polysulfide ions to give polysulfido complexes.² Related reactions were once used in university courses on qualitative inorganic analysis.

Stibnite has a structure similar to that of arsenic trisulfide, As₂S₃. The Sb(III) centers, which are pyramidal and three-coordinate, are linked via bent two-coordinate sulfide ions.

Uses

Stibnite has no significant uses, except as a precursor to antimony oxide, which is the most commonly marketed form of antimony. In ancient times, it was used as mascara called kohl.

Antimony trisulfide finds use in pyrotechnic compositions, namely in the glitter and fountain mixtures. Needle-like crystals, "Chinese Needle", are used in glitter compositions and white pyrotechnic stars. The "Dark Pyro" version is used in flash powders to increase their sensitivity and sharpen their report. It is also a component of modern safety matches. It was formerly used in flash compositions, but its use was abandoned due to toxicity and sensitivity to static electricity.[1]

Occurrence

Small deposits of stibnite are common, but large deposits are rare. It occurs in Canada, Mexico, Peru, Japan, China, Germany, Romania, Italy, France, England, Algeria, and Kalimantan, Borneo. In the United States it is found in Arkansas, Idaho, Nevada, California, and Alaska. Large iridescent stibnite crystals are found in Japan.^{citation needed}

Stibnite specimen at the American Museum of Natural History

As of May 2007, the largest specimen on public display (1000 pounds) is at the American Museum of Natural History.³⁴

See also

• List of minerals

References