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)
6
Zr
3
Ti
3
MnSi
51
O
144
(OH,H
2
O,Cl)
9
.[2][3] 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.[3] After alluaivite and labyrinthite it stands for third representative of the eudialyte group with essential titanium.[2]

Dualite
General
CategorySilicate mineral, Cyclosilicate
Formula
(repeating unit)
Na
30
(Ca,Na,Ce,Sr)
12
(Na,Mn,Fe,Ti)
6
Zr
3
Ti
3
MnSi
51
O
144
(OH,H
2
O,Cl)
9
IMA symbolDua[1]
Strunz classification9.CO.10
Dana classification64.1b.1.4
Crystal systemTrigonal
Crystal classDitrigonal pyramidal (3m)
H-M symbol: (3m)
Space groupR3m
Unit cella = 14.15, c = 60.72 [Å] (approximated); Z = 3
Identification
ColorYellow
Crystal habitanhedral grains
CleavageNone
FractureConchoidal
TenacityBrittle
Mohs scale hardness5
LusterVitreous
StreakWhite
DiaphaneityTransparent or Translucent
Density2.84 (measured), 2.81 (calculated; approximated)
Optical propertiesUniaxial (+)
Refractive indexnω=1.61, nε=1.61 (approximated)
PleochroismNone
Ultraviolet fluorescenceNo
References[2][3]

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.[3]

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.[3]

Notes on crystal structure

Dualite has doubled c value when compared to ordinary eudialyte. Its structural framework has 24 layers.[3]

References

  1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. Mindat, Dualite, http://www.mindat.org/min-27578.html
  3. 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


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