Rastsvetaevite
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]
Rastsvetaevite | |
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Tiny dark pink grains of rastsvetaevite in matrix. Field of view 3 mm. From: Rasvumchorr Mt, Khibiny Massif, Murmansk Oblast, Russia | |
General | |
Category | Silicate mineral, Cyclosilicate |
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 |
Specific gravity | 2.86 |
Optical properties | Uniaxial (+) |
Refractive index | nω=1.60 nε = 1.60 (approximated) |
References | [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]
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References
- 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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