Chemistry:Fettelite

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Fettelite
Fettelite-14124.jpg
Cluster of tiny fettelite crystals in a vug from Copiapó, Atacama Region, Chile
General
CategorySulfosalt mineral
Formula
(repeating unit)
Ag16HgAs4S15 (rruff) or
[Ag6As2S7]·[Ag10HgAs2S8] (mindat.org)
Strunz classification2.LA.30
Crystal systemMonoclinic
Crystal classSphenoidal (2)
(same H-M symbol)
Space groupC2
Unit cella = 15.00, c = 15.46 [Å]
V = 3014 Å3; Z = 8
Identification
Colordark violet to red
Crystal habitflakes, hexagonal, micaceous
Twinningintimately twinned with six twin domains
Cleavageperfect
Fracturesubconchoidal
Mohs scale hardness3.5
|re|er}}metallic
Streakdark vermillion
Diaphaneitysubopaque to opaque
Specific gravity6.29
Optical propertiesBiaxial, anisotrophism weak with strong red internal reflections
Refractive indexN(calc) = 1.74
Birefringencemoderate white to brownish gray
References[1][2][3]

Fettelite, also known as sanguinite, is a mercury-sulfosalt mineral with the chemical formula Ag16HgAs4S15. The mineral was first described by Wang and Paniagua (1996)[5] who named it after M. Fettel, a German field geologist who collected the first samples from Odenwald.[6] It was first collected in the Nieder-Beerbach mine, 10 km south of Darmstadt, Odenwald, Germany . Its normal occurrence is in hydrothermal veins, which can cut gabbro-diorite intrusives. It is closely related to other rare minerals like dervillite, daomanite, vaughanite and criddleite which are also found in the same type locality as fettelite.[3]

Fettelite occurs as clusters of hexagonal flakes. These flakes can get up to 0.2 mm across and around 5-10 µm thick. In more complex hexagonal tablets, somewhat larger sub parallel aggregates can be measured.[7] The birefringence of Fettelite is moderate white to grayish brown.[6]

References

  1. Mineralienatlas
  2. Mindat.org Accessed 4 November 2010
  3. 3.0 3.1 Jambor, John L.; Puziewicz, Jacek; Roberts, Andrew C. (1997). "New mineral name". American Mineralogist 82: 620–624. http://www.minsocam.org/msa/ammin/TOC/abstracts/1997_Abstracts/MJ97_Abstracts/Jambor_p620_97.pdf. 
  4. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine 85 (3): 291–320. doi:10.1180/mgm.2021.43. Bibcode2021MinM...85..291W. 
  5. Wang, N. and Paniagua, A. (1996) Fettelite, a new Hg-sulfosalt mineral from Odenwald. Neues Jahrbuch für Mineralogie Monatshefte, 82, 313–320.
  6. 6.0 6.1 Bindi, Luca; Keutsch, Frank N.; Francis, Carl A.; Menchetti, Silvio (2009). "Fettelite, {Ag6As2S7}{Ag10HgAs2S8} from Chañarcillo, Chile: Crystal structure, pseudosymmetry, twinning, and revised chemical formula". American Mineralogist 94: 609–615. doi:10.2138/am.2009.3096. http://www.minsocam.org/msa/ammin/TOC/Abstracts/2009_Abstracts/Apr09_Abstracts/Bindi_p609_09.pdf. 
  7. Mandarino, J.A (1997) Abstracts of new mineral description The Mineralogical Record, 28, 141-143.