Dualite
Dualite is a very rare and complex mineral of the eudialyte group, its complexity being expressed in its formula Na
30(Ca,Na,Ce,Sr)
12(Na,Mn,Fe,Ti)
6Zr
3Ti
3MnSi
51O
144(OH,H
2O,Cl)
9.[1][2] The formula is simplified as it does not show the presence of cyclic silicate groups.
The name of the mineral comes from its dual nature: zircono- and titanosilicate at once. Dualite has two modules in its structure: alluaivite one and eudialyte one.[2] After alluaivite and labyrinthite it stands for third representative of the eudialyte group with essential titanium.[1]
| Dualite | |
|---|---|
| General | |
| Category | Silicate mineral, Cyclosilicate |
| Formula (repeating unit) | Na 30(Ca,Na,Ce,Sr) 12(Na,Mn,Fe,Ti) 6Zr 3Ti 3MnSi 51O 144(OH,H 2O,Cl) 9 |
| Strunz classification | 9.CO.10 |
| Dana classification | 64.1b.1.4 |
| Crystal system | Trigonal |
| Crystal class | Ditrigonal pyramidal (3m) H-M symbol: (3m) |
| Space group | R3m |
| Unit cell | a = 14.15, c = 60.72 [Å] (approximated); Z = 3 |
| Identification | |
| Color | Yellow |
| Crystal habit | anhedral grains |
| Cleavage | None |
| Fracture | Conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 5 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent or Translucent |
| Density | 2.84 (measured), 2.81 (calculated; approximated) |
| Optical properties | Uniaxial (+) |
| Refractive index | nω=1.61, nε=1.61 (approximated) |
| Pleochroism | None |
| Ultraviolet fluorescence | No |
| References | [1][2] |
Occurrence and association
Dualite was found in peralkaline pegmatoid rock at Mt Alluaiv, Lovozero massif, Kola Peninsula Russia. It associates with aegirine, alkaline amphibole, cancrinite, eudialyte, K-Na feldspar, lamprophyllite, lomonosovite, lovozerite, nepheline, sodalite, sphalerite, villiaumite, and vuonnemite.[2]
Notes on chemistry
Dualite admixtures not mentioned in the formula are especially that of niobium, with lesser amount of aluminium, barium, potassium, neodymium and lanthanum. Dualite is chemically similar to labyrinthite and rastsvetaevite.[2]
Notes on crystal structure
Dualite has doubled c value when compared to ordinary eudialyte. Its structural framework has 24 layers.[2]
References
- Mindat, Dualite, http://www.mindat.org/min-27578.html
- Khomyakov, A.P., Nechelyustov, G.N., and Rastsvetaeva, R.K., 2009: Dualite, Na30(Ca,Na,Ce,Sr)12(Na,Mn,Fe,Ti)6Zr3Ti3MnSi51O144(OH,H2O,Cl)9, a new zircono-titanosilicate with a modular eudialyte-like structure from the Lovozero alkaline Pluton, Kola Peninsula, Russia. Geology of Ore Deposits 50(7), 574-582
Further reading
- Johnsen, O., Ferraris, G., Gault, R.A., Grice, D.G., Kampf, A.R., and Pekov, I.V., 2003. The nomenclature of eudialyte-group minerals. The Canadian Mineralogist 41, 785-794