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Khomyakovite

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Mineral of the eudialyte group
Khomyakovite
General
CategorySilicate mineral, cyclosilicate
Formula
(repeating unit)		Na12Sr3Ca6Fe3Zr3W(Si25O73)(O,OH,H2O)3(OH,Cl)2 (original form)
IMA symbolKmy
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  (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

Khomyakovite is an exceedingly rare mineral of the eudialyte group, with formula Na12Sr3Ca6Fe3Zr3W(Si25O73)(O,OH,H2O)3(OH,Cl)2. 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. Some niobium substitutes for tungsten in khomyakovite. Khomyakovite is an iron-analogue of manganokhomyakovite, the second mineral being a bit more common. 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).

Occurrence and association

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

Notes on chemistry

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

References

  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. ^ Mindat, Khomyakovite, http://www.mindat.org/min-7137.html
  3. ^ 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.


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