Dimorphite

General
Category| Sulfide mineral
Formula
(repeating unit)| As4S3
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
|re|er}}| adamantine
Streak| yellow
Diaphaneity| transparent
Specific gravity| 3.59
Optical properties| Biaxial (+)
Dispersion| strong
Ultraviolet fluorescence| none
Other characteristics| burns without residue
References| [1][2][3]

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 .[2] It has also been reported from Cerro de Pasco, Peru, and the Lavrion District Mines in Attica, Greece.[1]

## 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.

## References

1. ↑ 1.0 1.1 Dimorphite mineral information and data Mindat.org
2. ↑ 2.0 2.1 Handbook of Mineralogy
3. ↑ Webmineral data
4. ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine 85 (3): 291–320. doi:10.1180/mgm.2021.43. Bibcode: 2021MinM...85..291W.
5. ↑ Guarini G, Palmieri L, Scacchi A (1855) Chapter 5. Esame mineralogico-chimico delle produzioni dell'incendio, in Memoria sullo Incendio Vesuviano, Gaetano Nobile (Napoli) p. 165-200
6. ↑ 6.0 6.1 Wiberg, Egon, Nils Wiberg, and Arnold Frederick Holleman. Inorganic Chemistry. San Diego: Academic Press, 2001.
7. ↑ Tsiulyanu, D.; Golbam, G.; Kolomeyho, E.; Melnic, O. (1996). "Photoconductivity and optical absorption of dimorphite thin films". Physica Status Solidi B 197 (1): 61–64. doi:10.1002/pssb.2221970110. Bibcode: 1996PSSBR.197...61T.
8. ↑ Marian, S.; Potje-Kamloth, K.; Tsiulyanu, D.; Liess, H. -D. (2000). "Dimorphite based gas sensitive thin films". Thin Solid Films 359 (1): 108–112. doi:10.1016/S0040-6090(99)00707-5. Bibcode: 2000TSF...359..108M.

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