Manganokhomyakovite

Manganokhomyakovite
	Manganokhomyakovite
General
Category	Cyclosilicates
Formula; (repeating unit)	Na12Sr3Ca6Mn3Zr3W(Si25O73) ; (O,OH,H2O)3(OH,Cl)2 ; (original form)
Strunz classification	9.CO.10 (10 ed) ; 8/E.23-35 (8 ed)
Dana classification	64.1.2.6
Crystal system	Trigonal
Crystal class	Ditrigonal pyramidal (3m) ; (same H-M symbol)
Space group	R3m
Unit cell	a = 14.28, c = 30.12 [Å] (approximated); Z = 3
Identification
Color	Orange to orange-red
Crystal habit	pseudo-octahedra
Cleavage	None
Fracture	Uneven
Tenacity	Brittle
Mohs scale hardness	5-6
Luster	Vitreous
Streak	White
Diaphaneity	Transparent to translucent
Density	3.13 (measured), 3.17 (calculated)
Optical properties	Uniaxial (-)
Refractive index	nω=1.63, nε=1.63 (approximated)
Pleochroism	None
References	[1][2]

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]

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]

References

Mindat, Manganokhomyakovite, http://www.mindat.org/min-7137.html
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
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
"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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[Mindat-1] Mindat, Manganokhomyakovite, http://www.mindat.org/min-7137.html

[CanMin1-2] 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.