Dimorphite
Arsenic-sulfide mineral
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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 at temperatures of 70–80 °C (158–176 °F). Dimorphite was first discovered in such a fumarole near Naples, Italy in 1849 by the mineralogist Arcangelo Scacchi (1810–1893).[5] Since its discovery, dimorphite has been found in the Alacrán silver mine near Copiapó, Chile.[3] It has also been reported from Cerro de Pasco, Peru, and the Lavrion District Mines in Attica, Greece.[2]
| Dimorphite | |
|---|---|
| General | |
| Category | Sulfide mineral |
| Formula | As4S3 |
| IMA symbol | Dim[1] |
| Strunz classification | 2.FA.10 |
| Crystal system | Orthorhombic |
| Crystal class | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
| Space group | Pnma |
| Unit cell | a = 11.24, b = 9.90 c = 6.56 [Å]; Z = 4 |
| Identification | |
| Formula mass | 395.88 g/mol |
| Color | orange-yellow |
| Crystal habit | Groups of pyramidal crystals |
| Cleavage | none |
| Fracture | brittle |
| Mohs scale hardness | 1.5 |
| Luster | adamantine |
| Streak | yellow |
| Diaphaneity | transparent |
| Specific gravity | 3.59 |
| Optical properties | Biaxial (+) |
| Dispersion | strong |
| Ultraviolet fluorescence | none |
| Other characteristics | burns without residue |
| References | [2][3][4] |
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).[6]
Dimorphite can be synthesized by melting arsenic and sulfur together in the proper molar ratios in vacuum.[6]
Initial research indicates the possibility of using synthetic dimorphite in the development of gas sensors,[7][8] due to the semiconductive properties of dimorphite.