Golyshevite

{{Short description|Rare cyclosilicate mineral}}

{{infobox mineral

| name = Golyshevite

| category = Silicate mineral, cyclosilicate

| image = Golyshevite.jpg

| imagesize =

| alt =

| caption = 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

| formula = (Na,Ca)₁₀Ca₉(Fe³⁺,Fe²⁺)₂Zr₃NbSi₂₅O₇₂(CO₃)(OH)₃·H₂O (original form)

| IMAsymbol = Gsv{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}

| strunz = 9.CO.10

| dana = 64.1.6

| system = Trigonal

| class = Ditrigonal pyramidal (3m)
(same H-M symbol)

| symmetry = R3m

| unit cell = a = 14.23
c = 29.98 [Å] (approximated); Z = 3

| color = Brown to reddish-brown

| colour =

| habit = Grains and crystals

| twinning =

| cleavage = No

| fracture =

| tenacity = Brittle

| mohs =

| luster =

| streak =

| diaphaneity =

| gravity = 2.89 (measured)

| density =

| polish =

| opticalprop = Uniaxial (−)

| refractive = nω = 1.62, nε = 1.61 (approximated)

| birefringence =

| pleochroism = Green to pale yellow

| 2V =

| dispersion =

| extinction =

| length fast/slow =

| fluorescence =

| absorption =

| melt =

| fusibility =

| diagnostic =

| solubility =

| impurities =

| alteration =

| other =

| references =

}}

Golyshevite is a rare mineral of the eudialyte group,Mindat, Golyshevite, http://www.mindat.org/min-27418.html with the formula Na₁₀Ca₃Ca₆Zr₃Fe₂SiNb(Si₃O₉)₂(Si₉O₂₇)₂CO₃(OH)₃•H₂O. 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.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 The characteristic feature of golyshevite is calcium-rich composition, with calcium at two main sites instead of one site.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) Together with feklichevite, fengchengite, ikranite and mogovidite it is a ferric-iron-dominant representative of the group. It is chemically similar to mogovidite. Golyshevite was named after Russian crystallographer Vladimir Mikhailovich Golyshev.