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Fettelite

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Fettelite
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)
IMA symbolFtt[1]
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
Lustermetallic
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[2][3][4]

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.[4]

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

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  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ Mineralienatlas
  3. ^ Mindat.org Accessed 4 November 2010
  4. ^ a b Jambor, John L.; Puziewicz, Jacek; Roberts, Andrew C. (1997). "New mineral name" (PDF). American Mineralogist. 82: 620–624.
  5. ^ Wang, N. and Paniagua, A. (1996) Fettelite, a new Hg-sulfosalt mineral from Odenwald. Neues Jahrbuch für Mineralogie Monatshefte, 82, 313–320.
  6. ^ a b 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" (PDF). American Mineralogist. 94: 609–615. doi:10.2138/am.2009.3096. S2CID 53975716.
  7. ^ Mandarino, J.A (1997) Abstracts of new mineral description The Mineralogical Record, 28, 141-143.