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

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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

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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

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

References

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  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. ^ a b c Mindat, Dualite, http://www.mindat.org/min-27578.html
  3. ^ a b c d e f 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

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  • 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