Raslakite

Raslakite
	Red glassy raslakite in nepheline-syenite from the type locality: Karnasurt Mountain, Lovozero Massif, Northern Region, Russian Federation.
General
Category	Silicate mineral, Cyclosilicate
Formula; (repeating unit)	Na15Ca3Fe3(Na,Zr)3Zr3(Si,Nb)(Si25O73)(OH,H2O)3(Cl,OH) (original form)
Strunz classification	9.CO.10
Crystal system	Trigonal
Crystal class	Pyramidal (3) ; H-M symbol: (3)
Space group	R3
Unit cell	a = 14.23, c = 30.02 [Å]; Z = 3
Identification
Color	Brownish-red
Crystal habit	Grains
Cleavage	Imperfect
Fracture	Conchoidal
Tenacity	Brittle
Mohs scale hardness	5
Luster	Vitreous
Streak	White
Diaphaneity	Transparent
Specific gravity	2.95 (measured)
Optical properties	Uniaxial
Refractive index	nω=1.61, nε=1.61 (approximated)
References	[1][2]

Raslakite is a rare mineral of the eudialyte group with the formula Na₁₅Ca₃Fe₃(Na,Zr)₃Zr₃(Si,Nb)SiO(Si₉O₂₇)₂(Si₃O₉)₂(OH,H₂O)₃(Cl,OH). This formula is based on the original one, and is extended to show the presence of cyclic silicate groups. The additional silicon and oxygen shown in separation from the cyclic groups (in parentheses) are in fact connected with two 9-fold rings.[1] The mineral has lowered symmetry (space group R3, instead of more specific for the group R3m one),[2] similarly to some other eudialyte-group members: aqualite, labyrinthite, oneillite and voronkovite.[1] The specific feature of raslakite is, among others, the presence of sodium and zirconium at the M2 site. Raslakite was named after Raslak Cirques located nearby the type locality.[2]

Occurrence and association

Raslakite was discovered, together with ikranite, in peralkaline pegmatites of the Mt. Karnasurt, Lovozero massif, Kola Peninsula, Russia. Raslakite is associated with aegirine, fluorcaphite, kazakovite, lamprophyllite, microcline, nepheline, and terskite.[2]

Notes on chemistry

Beside main elements given in the formula, raslakite contains some potassium, strontium, manganese, magnesium, cerium, titanium, and aluminium, with minor amounts of lanthanum and hafnium.[2]

Notes on crystal structure

The M(1) site in raslakite is split into two sub-sites, where Fe and Ca are located. The M(2) site is occupied by sodium, manganese (both with coordination number 5), and zirconium (tetrahedral coordination).[2]

gollark: I am not aware of such an individual.

gollark: Well, if you don't start insisting that windows good FOSS bad again, sure.

gollark: We don't have a bot for that.

gollark: You can't really say "end of conversation" and expect people to agree with you. You *can* stop talking to them, but aren't.

gollark: I mean, it would make it funnier, and more profitable, sure.

References

Mindat, Raslakite, http://www.mindat.org/min-25687.html
Chukanov, N.V., Pekov, I.V., Zadov, A.E., Korovushkin, V.V., Ekimenkova, I.A., and Rastsvetaeva, R.K., 2003: Ikranite, (Na,H₃O)₁₅(Ca,Mn,REE)₆Fe³⁺₂Zr₃([],Zr)([],Si)Si₂₄O₆₆(O,OH)₆Cl·nH₂O and raslakite Na₁₅Ca₃Fe₃(Na,Zr)₃Zr₃(Si,Nb)(Si₂₅O₇₃)(OH,H₂O)₃(Cl,OH)-new eudialyte-group minerals from the Lovozero massif, Kola Peninsula. Zapiski Vserossiyskogo Mineralogicheskogo Obshchestva 132(5), 22–33 (in Russian, with English abstract)

This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.

[M-1] Mindat, Raslakite, http://www.mindat.org/min-25687.html

[Ch-2] Chukanov, N.V., Pekov, I.V., Zadov, A.E., Korovushkin, V.V., Ekimenkova, I.A., and Rastsvetaeva, R.K., 2003: Ikranite, (Na,H₃O)₁₅(Ca,Mn,REE)₆Fe³⁺₂Zr₃([],Zr)([],Si)Si₂₄O₆₆(O,OH)₆Cl·nH₂O and raslakite Na₁₅Ca₃Fe₃(Na,Zr)₃Zr₃(Si,Nb)(Si₂₅O₇₃)(OH,H₂O)₃(Cl,OH)-new eudialyte-group minerals from the Lovozero massif, Kola Peninsula. Zapiski Vserossiyskogo Mineralogicheskogo Obshchestva 132(5), 22–33 (in Russian, with English abstract)