Ikranite
A variety of Eudialyte group
What is Ikranite?
Ikranite is a member of the eudialyte group, named after the Shubinov Institute of Crystallography of the Russian Academy of Sciences. It is a cyclosilicate mineral that shows trigonal symmetry with the space group R3m, and is often seen with a pseudo-hexagonal habit. Ikranite appears as translucent and ranges in color from yellow to a brownish yellow. This mineral ranks a 5 on Mohs Scale of Hardness, though it is considered brittle, exhibiting conchoidal fracture when broken.
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Key Characteristics
Formation of Ikranite
Ikranite was first discovered on Mount Karnasurt (Kola Peninsula) in an agpaitic pegmatite, in the form of 1–2 cm grains. It is commonly associated with microcline, nepheline, lorenzenite, murmanite, lamprophyllite, and arfvedsonite. Tetranatrolite, and halloysite can also be found with it, though they occur at a later stage.
Composition of Ikranite
The crystal structure of ikranite can be described as a framework of three- and nine- member SiO4 tetrahedra rings, connected by Ca six-membered rings and Zn (Ti, or Nb) octahedra. Layers are constructed along the c axis as Si-Zr-Si-Ca. This repetition generates 12 layers, equal to ~30Å in size. Differing types cations, anions, anionic groups, and water molecules fill any pockets within the framework. A defining feature is the location of the M(3) and M(4) vacancies in the nine-membered rings. These cavities may be occupied with Si in the M(3b) location, Zr in the M(4a), and Zr, Nb, or Ti in the (M4b), though the probability of occupancy is low. The M(2a) and M(2b) locations are also uniquely occupied in ikranite. The M(2a) vacancy is seen occupied by Fe octahedra. Typically holding a five-membered polyhedra with Fe, the M(2b) position is occupied by Na cations. Ikranite also holds a significant amount of water in the space between the rings where an Na molecule is usually found. A distinctive feature is the oxonium groups that can also be found occupying Na sites. Ikranite's general formula thus becomes (Na,H3O)15(Ca,Mn,REE)6Fe3+2Zr3([ ],Zr)([ ],Si)Si24O66(O,OH)6Cl2-3H2O.
Quick Facts
Physical Properties
- Color
- brownish yellow to light brown
- Hardness (Mohs)
- 5
- Density
- 2.82 g/cm³
- Streak
- white
Chemical Properties
- Chemical Formula
- (Na,H3O)15(Ca,Mn2+)6Fe3+2Zr3[H0-3Si3O9)2(Si9O27)2SiO]Cl · 2-3H2O
- Elements
- Ca, Cl, Fe, H, Mn, Na, O, Si, Zr
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