Rastsvetaevite

Rastsveatevite is a rare mineral of the eudialyte group with the chemical formula Na₂₇K₈Ca₁₂Fe₃Zr₆Si₄[Si₃O₉]₄[Si₉O₂₇]₄(O,OH,H₂O)₆Cl₂. Its structure is modular.^[3] It is only the third member of the group after andrianovite and davinciite with essential (site-dominating) potassium.^[2] Potassium and sodium enter both N4 and M2 sites.^[4] The mineral is named after Russian crystallographer Ramiza K. Rastsvetaeva.^[2]

Rastsvetaevite
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
IMA symbol	Rtv[1]
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	[2]

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.^[2]

Notes on crystal structure

The c unit cell parameter in rastsvetaevite is doubled.^[2]