Rastsvetaevite

Rastsvetaevite
General
Category Silicate mineral, Cyclosilicate
Formula
(repeating unit)
Na27K8Ca12Fe3Zr6Si4[Si3O9]4[Si9O27]4(O,OH,H2O)6Cl2
Strunz classification 9.CO.10
Dana classification 64.1b.1.2
Crystal system Trigonal
Unit cell a = 14.25, c = 60.97 [Å] (approximated); Z = 3
Identification
Color Reddish-pink
Crystal habit irregular grains
Crystal symmetry Trigonal - ditrigonal pyramidal
H-M symbol (3m)
Space group: R3m
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. 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, D.G., Kampf, A.R., and Pekov, I.V., 2003. The nomenclature of eudialyte-group minerals. The Canadian Mineralogist 41, 785-794
This article is issued from Wikipedia - version of the Wednesday, April 27, 2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.