Andrianovite

Andrianovite is a very rare mineral of the eudialyte group,^[2] with formula Na₁₂(K,Sr,Ce)₆Ca₆(Mn,Fe)₃Zr₃NbSi(Si₃O₉)₂(Si₉O₂₇)₂O(O,H₂O,OH)₅.^[3][2] The original formula was extended to show the presence of cyclic silicate groups and silicon at the M4 site, according to the nomenclature of eudialyte group.^[4] Andrianovite is unique among the eudialyte group in being potassium-rich (other eudialyte-group species with essential K are davinciite and rastsvetaevite^[2]). It is regarded as potassium analogue of kentbrooksite,^[3] but it also differs from it in being oxygen-dominant rather than fluorine-dominant.^[2] Also, the coordination number of Na in this representative is enlarged from 7 to 9. The name of the mineral honors Russian mathematician and crystallographer Valerii Ivanovich Andrianov.^[3]

Andrianovite
Andrianovite found in Russia
General
Category	Silicate mineral, Cyclosilicate
Formula	Na12(K,Sr,Ce)3Ca6Mn3Zr3Nb(Si25O73)(O,H2O,OH)5 (original form)
IMA symbol	Adv[1]
Strunz classification	9.CO.10
Dana classification	64.1.2.4
Crystal system	Trigonal
Crystal class	Ditrigonal pyramidal (3m) H-M symbol: (3m)
Space group	R3m
Unit cell	a = 14.28, c = 30.24 [Å] (approximated); Z = 3
Identification
Color	Light yellow
Crystal habit	intergrowths (rims) with eudialyte
Cleavage	(001), imperfect
Fracture	Step-like
Tenacity	Brittle
Mohs scale hardness	5
Luster	Vitreous
Streak	White
Diaphaneity	Transparent
Density	2.93 (measured), 3.02 (calculated)
Optical properties	Uniaxial (−)
Refractive index	nω = 1.62, nε = 1.62 (approximated)
Pleochroism	None
Ultraviolet fluorescence	No
Common impurities	Sr, Ce, Fe
References	[2][3]

Occurrence and association

Andrianovite was discovered in pegmatites of Koashva open pit, Khibiny massif, Kola Peninsula. Russia. It coexists with aegirine, lamprophyllite, lomonosovite, microcline, mosandrite, natrolite, sodalite (silicates) and villiaumite.^[3]

Notes on chemistry

The formula of andrianovite is devoid of some substituting elements and group, the most important being carbonate and chlorine. Minor substituting elements are lanthanum, neodymium, yttrium, titanium, barium, hafnium and aluminium.^[3]