Chrysothallite

Chrysothallite is a rare thallium-bearing chloride mineral with the formula K6Cu6Tl3+Cl17(OH)4•H2O.[2][3] Chrysothallite is unique in being only the second mineral with essential trivalent thallium,[2] a feature shared with natural thallium(III) oxide, avicennite.[4] Another examples of natural thallium chlorides are steropesite, Tl3BiCl6, and lafossaite, TlCl.[5][6] Chrysothallite is one of numerous fumarolic minerals discovered among fumarolic sites of the Tolbachik volcano, Kamchatka, Russia[7] The mineral is named in allusion to its colour and thallium content.[2]

Chrysothallite
General
CategoryHalide mineral
Formula
(repeating unit)		K6Cu6Tl3+Cl17(OH)4•H2O
Crystal systemTetragonal
Crystal classDitetragonal dipyramidal (4/mmm)
H-M symbol: (4/m 2/m 2/m)
Space groupI4/mmm
Unit cella = 11.37 Å, b = 26.21 Å (approximated); Z = 4
Identification
ColorGolden-yellow to light yellow
Crystal habittabular
CleavageNone
FractureUneven
TenacityBrittle
LusterVitreous
StreakWhite
DiaphaneityTransparent
Density2.95 (measured)
Optical propertiesUniaxial (+)
Refractive indexω=1.72, ε=1.73 (approximated)
References[1][2][3]

Notes on chemistry

Chrysothallite contains a relative high amount of zinc admixture. Zinc is substituting for copper.[2]

Association and origin

Chrysothallite may be associated with many other minerals:[2]

Crystal structure

The crystal structure of chrysothallite is unique. Its building elements are:[2]

  • layer of distorted CuCl4(OH)2 octahedra, in which the octahedra share edges
  • isolated Tl-centered TlCl6 octahedra
  • isolated Tl-centered TlCl4(H2O)2 octahedra
  • KCl6 and KCl9 polyhedra, that connect all the above elements

Origin

Chrysothallite is supposed to be a product of interaction of relatively high-temperature fumarolic minerals with fumarolic gas and atmospheric water, that takes place in temperatures up to 150 °C (302 °F).

References
  1. Mineralienatlas
  2. Pekov, I.V., Zubkova, N.v., Belakovskiy, D.I., Yapaskurt, V.O., Vigasina, M.F., Lykova, I.S., Sidorov, E.G., and Pushcharovsky, D.Yu., 2015. Chrysothallite K6Cu6Tl3+Cl17(OH)4.H2O, a new mineral species from the Tolbachik volcano, Kamchatka, Russia. Mineralogical Magazine 79(2), 365-376
  3. "Chrysothallite: Chrysothallite mineral information and data". Mindat.org. Retrieved 2016-03-11.
  4. "Avicennite: Avicennite mineral information and data". Mindat.org. Retrieved 2016-03-11.
  5. "Steropesite: Steropesite mineral information and data". Mindat.org. Retrieved 2016-03-11.
  6. "Lafossaite: Lafossaite mineral information and data". Mindat.org. Retrieved 2016-03-11.
  7. "Tolbachik volcano, Kamchatka Oblast', Far-Eastern Region, Russia - Mindat.org". Mindat.org. Retrieved 2016-03-11.


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