Dimorphite

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
Luster 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 tetraarsenic trisulfide (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 mineralologist Arcangelo Scacchi (1810–1893). 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).[4]

Dimorphite can be synthesized by melting arsenic and sulfur together in the proper molar ratios in vacuum.[4]

Initial research indicates the possibility of using synthetic dimorphite in the development of gas sensors,[5][6] due to the semiconductive properties of dimorphite.

References

  1. 1 2 Dimorphite mineral information and data Mindat.org
  2. 1 2 Handbook of Mineralogy
  3. ↑ Webmineral data
  4. 1 2 Wiberg, Egon, Nils Wiberg, and Arnold Frederick Holleman. Inorganic Chemistry. San Diego: Academic Press, 2001.
  5. ↑ 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. Bibcode:1996PSSBR.197...61T. doi:10.1002/pssb.2221970110.
  6. ↑ Marian, S.; Potje-Kamloth, K.; Tsiulyanu, D.; Liess, H. -D. (2000). "Dimorphite based gas sensitive thin films". Thin Solid Films. 359 (1): 108–112. Bibcode:2000TSF...359..108M. doi:10.1016/S0040-6090(99)00707-5.
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