Davinciite

Davinciite is a very rare mineral of the eudialyte group,[1][2] with the simplified formula Na12K3Ca6Fe32+Zr3(Si26O73OH)Cl2.[1][3] The formula given does not show the presence of cyclic silicate groups. The mineral was named after Leonardo da Vinci[3] to refer to the atypical geometrical forms he tended to use, compared by the authors of the mineral description to the atypical (not ideally centrosymmetrical) geometry of the Davinciite structure. The other quite atypical feature of Davinciite is its lavender colour, while the typical eudialyte is rather pink or red.[2]

Davinciite
General
CategorySilicate mineral, Cyclosilicate
Formula
(repeating unit)		Na12K3Ca6Fe2+3Zr3(Si26O73OH)Cl2 (original form)
Crystal systemTrigonal
Crystal classDitrigonal pyramidal (3m)
H-M symbol: (3m)
Space groupR3m
Unit cella = 14.29, c = 30.03 [Å] (approximated), Z = 3
Identification
ColourDark lavender
Crystal habitinclusions in rastsvetaevite
CleavageNone
FractureConchoidal
TenacityBrittle
Mohs scale hardness5
LusterVitreous
StreakWhite
DiaphaneityTransparent
Density2.82 (measured), 2.85 (calculated; approximated)
Optical propertiesUniaxial (+)
Refractive indexnω=1.61, nε=1.61 (approximated)
PleochroismNone
Ultraviolet fluorescenceNo
Common impuritiesSr, Mn, Ti, H2O
References[1][2]

Occurrence and association

Davinciite was discovered in hyperagpaitic (highly alkaline) pegmatite at Mt. Rasvmuchorr, Khibiny massif, Kola Peninsula, Russia. Aegirine, delhayelite, nepheline, potassium feldspar, shcherbakovite, sodalite (silicates), djerfisherite, rasvumite (sulfides), nitrite, nacaphite, and villiaumite are associated minerals.[2]

Notes on chemistry

Impurities in davinciite include strontium, manganese, titanium, with minor aluminium, barium, hafnium, and niobium. Some water is also present.[2]

References
  1. "Davinciite: Davinciite mineral information and data". Mindat.org. Retrieved 2016-03-08.
  2. Khomyakov, A.P.; Nechelyustov, G.N.; Rastsvetaeva, R.K.; Rozenberg, K.A. (2012). "Davinciite, Na12K3Ca6Fe2+3Zr3(Si26O73OH)Cl2, a new K, Na-ordered mineral of the eudialyte group from the Khibiny alkaline massif, Kola Peninsula, Russia". Zap. Ross. Mineral. Obshch. (in Russian and English). 141 (2): 10–21. doi:10.1134/S1075701513070076.
  3. "Davinciite" (PDF). HandbookofMineralogy.org. Retrieved March 1, 2016.


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