Manganokhomyakovite

Manganokhomyakovite is a very rare mineral of the eudialyte group,[1] with formula Na12Sr3Ca6Mn3Zr3WSi(Si9O27)2(Si3O9)2O(O,OH,H2O)3(OH,Cl)2.[2] This formula is in extended form (based on the original one), to show the presence of cyclic silicate groups and domination of silicon at the M4 site, basing on the nomenclature of the eudialyte group.[3] Some niobium substitutes for tungsten in khomyakovite. As suggested by its name, manganokhomyakovite is a manganese-analogue of khomyakovite, the latter being more rare.[2] The two minerals are the only group representatives, beside taseqite, with species-defining strontium, although many other members display strontium diadochy. Manganokhomyakovite is the third eudialyte-group mineral with essential tungsten (after johnsenite-(Ce) and khomyakovite).[1]

Manganokhomyakovite
Manganokhomyakovite
General
CategoryCyclosilicates
Formula
(repeating unit)		Na12Sr3Ca6Mn3Zr3W(Si25O73)
(O,OH,H2O)3(OH,Cl)2
(original form)
Strunz classification9.CO.10 (10 ed)
8/E.23-35 (8 ed)
Dana classification64.1.2.6
Crystal systemTrigonal
Crystal classDitrigonal pyramidal (3m)
(same H-M symbol)
Space groupR3m
Unit cella = 14.28, c = 30.12 [Å] (approximated); Z = 3
Identification
ColorOrange to orange-red
Crystal habitpseudo-octahedra
CleavageNone
FractureUneven
TenacityBrittle
Mohs scale hardness5-6
LusterVitreous
StreakWhite
DiaphaneityTransparent to translucent
Density3.13 (measured), 3.17 (calculated)
Optical propertiesUniaxial (-)
Refractive indexnω=1.63, nε=1.63 (approximated)
PleochroismNone
References[1][2]

Occurrence and association

Manganokhomyakovite, khomyakovite, johnsenite-(Ce) and oneillite are four eudialyte-group minerals discovered in alkaline rocks of Mont Saint-Hilaire, Quebec, Canada.[4] Association of manganokhomyakovite is rich and includes: aegirine, albite, analcime, annite, kupletskite, microcline, natrolite, sodalite, titanite, wöhlerite, zircon, cerussite, galena, molybdenite, pyrite, pyrrhotite, and sphalerite.[2]

Notes on chemistry

Impurities in manganokhomyakovite include niobium and iron, with traces of rare earth elements, hafnium, titanium, tantalum, and aluminium.[2]

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References
  1. Mindat, Manganokhomyakovite, http://www.mindat.org/min-7137.html
  2. 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
  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
  4. "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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