Golyshevite

Golyshevite is a rare mineral of the eudialyte group,[1] with formula Na10Ca3Ca6Zr3Fe2SiNb(Si3O9)2(Si9O27)2CO3(OH)3•H2O.[2] The original formula was extended to show both the presence of cyclic silicate groups and silicon at the M4 site, according to the nomenclature of the eudialyte group.[3] The characteristic feature of golyshevite is calcium-rich composition, with calcium at two main sites instead of one site.[2] Together with feklichevite, fengchengite, ikranite and mogovidite it is a ferric-iron-dominant representative of the group.[1] It is chemically similar to mogovidite.[1][2] Golyshevite was named after Russian crystallographer Vladimir Mikhailovich Golyshev.[2]

Golyshevite
Golyshevite crystals in matrix, some of them showing a pseudohexagonal section, with the typical yellowish-brown zircon-like colour. Locality: Kovdor Phlogopite Mine, Kovdor Massif, Northern Region, Russian Federation Size: 2.3 × 2.1 × 1.5 cm
General
CategorySilicate mineral, Cyclosilicate
Formula
(repeating unit)		(Na,Ca)10Ca9(Fe3+,Fe2+)2Zr3NbSi25O72(CO3)(OH)3·H2O (original form)
Strunz classification9.CO.10
Dana classification64.1.6
Crystal systemTrigonal
Crystal classDitrigonal pyramidal (3m)
(same H-M symbol)
Space groupR3m
Unit cella = 14.23
c = 29.98 [Å] (approximated); Z = 3
Identification
ColorBrown to reddish-brown
Crystal habitgrains and crystals
CleavageNo
TenacityBrittle
Specific gravity2.89 (measured)
Optical propertiesUniaxial (-)
Refractive indexnω 1.62, nε=1.61 (approximated)
Pleochroismgreen to pale yellow
References[1][2]

Occurrence and association

Golyshevite and mogovidite were found in calcium-bearing peralkaline pegmatites of the Kovdor massif, Kola Peninsula, Russia. Minerals associated with golyshevite are aegirine-augite, calcite, cancrinite, hedenbergite, orthoclase, pectolite, tacharanite, and thomsonite-Ca.[2]

Notes on chemistry

Impurities in golyshevite include chlorine, potassium, manganese, aluminium, cerium and lanthanum.[2]

Notes on crystal structure

Calcium in golyshevite is present at M(1) and N(4) sites.[2]

References
  1. Mindat, Golyshevite, http://www.mindat.org/min-27418.html
  2. Chukanov, N.V., Moiseyev, M.M., Rastsvetayeva, R.K., Rozenberg, K.A., and Zadov, A.E., 2005. Golyshevite (Na,Ca)10Ca9(Fe3+,Fe2+)2Zr3NbSi25O72(CO3)(OH)3·H2O, and Mogovidite, Na9(Ca,Na)6Ca6(Fe3+,Fe2+)2Zr3[]Si25O72(CO3)(OH,H2O)4, new eudialyte-group minerals from calcium-rich agpaitic pegmatites of the Kovdor massif, Kola Peninsula. Zapiski Rossiyskogo Mineralogicheskogo Obshchestva 134(6), 36-47 (in Russian, with English abstract)
  3. Johnsen, O., Ferraris, G., Gault, R.A., Grice, D.G., Kampf, A.R., and Pekov, I.V., 2003. The nomenclature of eudialyte-group minerals. The Canadian Mineralogist 41, 785-794
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