Dimorphite, chemical name arsenic sesquisulfide (As₄S₃), is a very rare orange-yellow arsenic sulfide mineral. In nature, dimorphite forms primarily by deposition in volcanic

fumaroles A fumarole (or fumerole) is a vent in the surface of the Earth or other rocky planet from which hot volcanic gases and vapors are emitted, without any accompanying liquids or solids. Fumaroles are characteristic of the late stages of volcani ...

at temperatures of 70–80 °C (158–176 °F). Dimorphite was first discovered in such a fumarole near Naples, Italy in 1849 by the mineralologist

Arcangelo Scacchi Arcangelo Scacchi (9 February 1810 – 11 October 1893) was an Italian physician, mineralogist, malacology, malacologist, and naturalist. He served as a professor of mineralogy at the University of Naples Federico II, University of Naples. Between ...

(1810–1893). Since its discovery, dimorphite has been found in the Alacrán silver mine near

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. It has also been reported from

Cerro de Pasco Cerro de Pasco is a city in central Peru, located at the top of the Andean mountains. It is the capital of the Pasco region, and an important mining center. At elevation, it is one of the highest cities in the world, and the highest or the sec ...

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, and the Lavrion District Mines in

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Properties and applications

Dimorphite has two crystal forms, Α- and Β-. This property gives rise to its name, which comes from the Greek for "two" and "form." Dimorphite transitions between its α- and β- forms at around 130 °C (266 °F). Dimorphite can be synthesized by melting arsenic and sulfur together in the proper molar ratios in vacuum.Wiberg, Egon, Nils Wiberg, and Arnold Frederick Holleman. ''Inorganic Chemistry.'' San Diego: Academic Press, 2001. Initial research indicates the possibility of using synthetic dimorphite in the development of gas sensors, due to the semiconductive properties of dimorphite.

References

{{Reflist Arsenic minerals Sulfide minerals Orthorhombic minerals Minerals in space group 62