Dualite

Short description: Mineral of the eudialyte group

Dualite

General
Category| Silicate mineral, cyclosilicate
Formula
(repeating unit)| Na30(Ca,Na,Ce,Sr)12(Na,Mn,Fe,Ti)6Zr3Ti3MnSi51O144(OH,H2O,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
|re|er}}| 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]

Dualite is a very rare and complex mineral of the eudialyte group, its complexity being expressed in its formula Na30(Ca,Na,Ce,Sr)12(Na,Mn,Fe,Ti)6Zr3Ti3MnSi51O144(OH,H2O,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]

## Contents

* 1 Occurrence and association
* 2 Notes on chemistry
* 3 Notes on crystal structure
* 4 References
* 5 Further reading

## 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

1. ↑ 1.0 1.1 1.2 Mindat, Dualite, http://www.mindat.org/min-27578.html
2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 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
3. ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine 85 (3): 291–320. doi:10.1180/mgm.2021.43. Bibcode: 2021MinM...85..291W.

## 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

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