Stibnite

Stibnite is a vital sulfide mineral known as antimony trisulfide (Sb2S3). It serves as the primary source for the metalloid antimony. This substance is a soft, metallic grey crystalline solid. It belongs to an orthorhombic space group, which describes its crystal structure. While fresh stibnite appears grey, it can turn black on the surface. This change happens due to oxidation when the mineral is exposed to air.

The internal structure of stibnite is quite complex. It is similar to the structure found in arsenic trisulfide (As2S3). In this mineral, the antimony (Sb(III)) centers are three-coordinate and shaped like pyramids. These pyramids link together using bent, two-coordinate sulfide ions. Some scientific studies suggest a different arrangement for the coordination polyhedra. These studies propose that antimony may have SbS7 coordination. This would involve (3+4) coordination at the M1 site and (5+2) at the M2 site. Certain secondary bonds also help provide cohesion through packing.

Stibnite possesses unique physical and chemical properties. It has a specific band gap of 1.88 eV at room temperature. Because of this, the mineral acts as a photoconductor. A photoconductor is a material that can conduct electricity when it is hit by light. However, users must be careful because stibnite is toxic if it is ingested. The symptoms of this toxicity are very similar to those caused by arsenic poisoning.

Humans have used stibnite for many thousands of years. Since approximately 3000 BC, people in the Mediterranean used stibnite powder. They mixed the powder with fat or other materials to create a cosmetic called kohl. This paste was used to darken eyebrows and eyelashes. It was also used to draw lines around the eyes. In protodynastic ancient Egypt, stibnite was used as both a medicine and a cosmetic. The Sunan Abi Dawood even records that the prophet Muhammad spoke of antimony as a way to clear vision.

In the 17th century, stibnite played a role in the study of alchemy. An alchemist named Eirenaeus Philalethes, also known as George Starkey, wrote about it. He described stibnite in his alchemical commentary on Sir George Ripley's Epistle. Starkey used the mineral as a precursor to what he called philosophical mercury. He believed this mercury was a precursor to the legendary philosopher's stone. Historically, the Romans also used stibnite from Dacia to produce colourless glass. This specific use ended when the Roman Empire lost that province.

Today, stibnite is frequently used in pyrotechnic compositions. It is a key ingredient in glitter and fountain mixtures. Specifically, needle-like crystals known as "Chinese needles" are used in white pyrotechnic stars. A "dark pyro" version of the mineral is used in flash powders. This version helps increase sensitivity and sharpens the report of the explosion. Stibnite is also a component in modern safety matches. It was once used in flash compositions, but this was abandoned. This change happened because the mineral is toxic and sensitive to static electricity.

Stibnite occurs naturally in hydrothermal deposits. These are areas where hot, mineral-rich water moves through the Earth's crust. It is often found alongside other minerals like realgar, orpiment, and cinnabar. It can also appear with galena, pyrite, marcasite, and arsenopyrite. Other associated minerals include cervantite, stibiconite, calcite, ankerite, barite, and chalcedony. While small deposits are common, very large deposits are quite rare. The Xikuangshan mine is the world's largest deposit of antimony. It yields high-quality crystals alongside calcite.

Stibnite is found in many different countries across the globe. It occurs in Canada, Mexico, Peru, Japan, Germany, Romania, Italy, France, England, Algeria, and Borneo. In the United States, it is found in Arkansas, Idaho, Nevada, California, and Alaska. Some very large specimens exist for study. As of May 2007, the largest specimen on public display weighed 1000 pounds. This massive specimen is located at the American Museum of Natural History. The largest single crystals ever documented measured roughly 60 by 5 by 5 cm. These large crystals have come from Japan, France, and Germany.