Dimorphite
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). Since its discovery, dimorphite has been found in the Alacrán silver mine near Copiapó, Chile. It has also been reported from Cerro de Pasco, Peru, and the Lavrion District Mines in Attica, Greece.
| Dimorphite | |
|---|---|
| General | |
| Category | Sulfide mineral |
| Formula (repeating unit) | As4S3 |
| IMA symbol | Dim |
| 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 | |
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