Rastsvetaevite

Rastsvetaevite
General
Category	Silicate mineral, Cyclosilicate
Formula; (repeating unit)	Na27K8Ca12Fe3Zr6 ; Si4[Si3O9]4[Si9O27]4(O,OH,H2O)6Cl2
Strunz classification	9.CO.10
Dana classification	64.1b.1.2
Crystal system	Trigonal
Crystal class	Ditrigonal pyramidal (3m) ; H-M symbol: (3m)
Space group	R3m
Unit cell	a = 14.25, c = 60.97 [Å] (approximated); Z = 3
Identification
Color	Reddish-pink
Crystal habit	irregular grains
Fracture	Conchoidal
Tenacity	Brittle
Mohs scale hardness	5-6
Luster	Vitreous
Streak	White
Diaphaneity	Transparent
Density	2.86 g/cm3 (measured)
Optical properties	Uniaxial (+)
Refractive index	nω=1.60 nε = 1.60 (approximated)
References	[1]

Rastsveatevite is a rare mineral of the eudialyte group with the formula Na₂₇K₈Ca₁₂Fe₃Zr₆Si₄[Si₃O₉]₄[Si₉O₂₇]₄(O,OH,H₂O)₆Cl₂. Its structure is modular.^[2] It is only the third member of the group after andrianovite and davinciite with essential (site-dominating) potassium.^[1] Potassium and sodium enter both N4 and M2 sites.^[3] The mineral is named after Russian crystallographer Ramiza K. Rastsvetaeva.^[1]

Occurrence and association

Rastsvetaevite was originally found in hyperagpaitic (ultra-alkaline) pegmatite at Mt. Rasvumchorr, Khibiny massif, Kola Peninsula, Russia. Associated minerals are aegirine, nacaphite, nepheline, natrite, schcherbakovite, sodalite, villiaumite, and rasvumite.^[1]

Notes on crystal structure

The c unit cell parameter in rastsvetaevite is doubled.^[1]

References

1 2 3 4 5 Mindat, http://www.mindat.org/min-26586.html
↑ Khomyakov, A.P.; Nechelyustov, G.N.; Arakcheeva, A.V. (2006). "Rastsvetaevite, Na₂₇K₈Ca₁₂Fe₃Zr₆Si₄[Si₃O₉]₄[Si₉O₂₇]₄(O,OH,H₂O)₆Cl₂, a new mineral with a modular eudialyte-like structure and crystal-chemical systematics of the eudialyte group". Proceedings of the Russian Mineralogical Society. 135 (1): 49–65.
↑ Johnsen, O.; Ferraris, G.; Gault, R. A.; Grice, J. D.; Kampf, A. R.; Pekov, I. V. (2003-06-01). "The nomenclature of eudialyte-group minerals". The Canadian Mineralogist. 41 (3): 785–794. doi:10.2113/gscanmin.41.3.785. ISSN 0008-4476.

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[M-1] 1 2 3 4 5 Mindat, http://www.mindat.org/min-26586.html

[2] Khomyakov, A.P.; Nechelyustov, G.N.; Arakcheeva, A.V. (2006). "Rastsvetaevite, Na₂₇K₈Ca₁₂Fe₃Zr₆Si₄[Si₃O₉]₄[Si₉O₂₇]₄(O,OH,H₂O)₆Cl₂, a new mineral with a modular eudialyte-like structure and crystal-chemical systematics of the eudialyte group". Proceedings of the Russian Mineralogical Society. 135 (1): 49–65.

[3] Johnsen, O.; Ferraris, G.; Gault, R. A.; Grice, J. D.; Kampf, A. R.; Pekov, I. V. (2003-06-01). "The nomenclature of eudialyte-group minerals". The Canadian Mineralogist. 41 (3): 785–794. doi:10.2113/gscanmin.41.3.785. ISSN 0008-4476.