Khomyakovite is an exceedingly rare mineral of the eudialyte group, with formula Na12Sr3Ca6Fe3Zr3W(Si25O73)(O,OH,H2O)3(OH,Cl)2.[2][3] The original formula was extended to show the presence of both the cyclic silicate groups and M4-site silicon, according to the nomenclature of the eudialyte group.[4] Some niobium substitutes for tungsten in khomyakovite. Khomyakovite is an iron-analogue of manganokhomyakovite, the second mineral being a bit more common.[3] The two minerals are the only group representatives, beside taseqite, with species-defining strontium, although many other members display strontium diadochy. Khomyakovite is the third eudialyte-group mineral with essential tungsten (after johnsenite-(Ce) and manganokhomyakovite).[2]

Khomyakovite
General
CategorySilicate mineral, cyclosilicate
Formula
(repeating unit)
Na12Sr3Ca6Fe3Zr3W(Si25O73)(O,OH,H2O)3(OH,Cl)2 (original form)
IMA symbolKmy[1]
Strunz classification9.CO.10 (10 ed)
8/E.23-30 (8 ed)
Dana classification64.1.2.5
Crystal systemTrigonal
Crystal classDitrigonal pyramidal (3m)
H-M symbol: (3m)
Space groupR3m
Unit cella = 14.30, c = 30.08 [Å] (approximated); Z = 3
Identification
ColorOrange to orange-red
Crystal habitAggregates (anhedral to subhedral)
CleavageNone
FractureUneven
TenacityBrittle
Mohs scale hardness5–6
LusterVitreous
StreakWhite
DiaphaneityTransparent to translucent
Density3.14 (calculated)
Optical propertiesUniaxial (−)
Refractive indexnω = 1.63, nε = 1.63 (approximated)
PleochroismNone
References[2][3]

Occurrence and association

edit

Khomyakovite, manganokhomyakovite, johnsenite-(Ce) and oneillite are four eudialyte-group minerals with type locality in Mont Saint-Hilaire, Quebec, Canada.[5] Khomyakovite itself is associated with analcime, annite, natrolite, titanite, calcite, and pyrite.[3]

Notes on chemistry

edit

Impurities in khomyakovite include niobium, potassium and manganese, with minor rare earth elements, magnesium, titanium, hafnium and aluminium.[3]

References

edit
  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. ^ a b c Mindat, Khomyakovite, http://www.mindat.org/min-7137.html
  3. ^ a b c d e Johnsen, O., Gault, R.A., Grice, J.D., and Ercit, T.S., 1999: Khomyakovite and manganokhomyakovite, two new members of the eudialyte group from Mont Saint-Hilaire, Quebec, Canada. The Canadian Mineralogist 37, 893–899
  4. ^ 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
  5. ^ "Poudrette quarry (Demix quarry; Uni-Mix quarry; Desourdy quarry; Carrière Mont Saint-Hilaire), Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Québec, Canada - Mindat.org". Mindat.org. Retrieved 2016-03-11.