Georgbarsanovite

Georgbarsanovite is a very rare mineral of the eudialyte group,^[2] formerly known under unaccepted name as barsanovite, with formula Na₁₂(Mn,Sr,REE)₃Ca₆Fe₃²⁺Zr₃NbSi(Si₃O₉)₂(Si₉O₂₇)₂O₄Cl₂·H₂O.^[3] The original formula was extended to show the presence of cyclic silicate groups and the domination of silicon at the M4 site.^[4] "REE", standing for rare earth elements, is dominated by cerium. Georgbarsanovite is characterized in dominance of manganese at the N4 site.^[3] It also differs from most other accepted group representatives in its colour. The mineral was found in nepheline pegmatite near Petrelius River, Khibiny massif, Kola Peninsula, Russia.^[2] It is named after Russian mineralogist Georg Barsanov.^[3]

Georgbarsanovite
Georgbarsanovite
General
Category	Silicate mineral, Cyclosilicate
Formula	Na12(Mn,Sr,REE)3Ca6Fe32+Zr3NbSi25O76Cl2·H2O (original form)
IMA symbol	Gba[1]
Strunz classification	9.CO.10 (10 ed) 8/E.23-15 (8 ed)
Dana classification	64.1.2.2
Crystal system	Trigonal
Crystal class	Ditrigonal pyramidal (3m) (same H-M symbol)
Space group	R3m
Unit cell	a = 14.26, c = 29.95 [Å] (approximated); Z = 3
Identification
Color	Yellow-green
Crystal habit	pseudo-octahedra
Cleavage	No
Fracture	Uneven
Tenacity	Brittle
Luster	Vitreous
Streak	White
Diaphaneity	Transparent
Optical properties	Uniaxial (-)
Refractive index	nω 1.64, nε=1.63 (approximated)
Pleochroism	green to pale yellow
Common impurities	F, K, Y
References	[2][3]

Notes on chemistry

Georgbarsanovite contains admixtures of fluorine, potassium and yttrium, with traces of titanium, hafnium, and barium.^[3]