Davinciite

Davinciite
General
Category Silicate mineral, Cyclosilicate
Formula
(repeating unit)
Na12K3Ca6Fe2+3Zr3(Si26O73OH)Cl2 (original form)
Crystal system Trigonal
Crystal class Ditrigonal pyramidal (3m)
H-M symbol: (3m)
Space group R3m
Unit cell a = 14.29, c = 30.03 [Å] (approximated), Z = 3
Identification
Color Dark lavender
Crystal habit inclusions in rastsvetaevite
Cleavage None
Fracture Conchoidal
Tenacity Brittle
Mohs scale hardness 5
Luster Vitreous
Streak White
Diaphaneity Transparent
Density 2.82 (measured), 2.85 (calculated; approximated)
Optical properties Uniaxial (+)
Refractive index nω=1.61, nε=1.61 (approximated)
Pleochroism None
Ultraviolet fluorescence No
Common impurities Sr, Mn, Ti, H2O
References [1][2]

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 address untypical geometrical forms he tend to use, compared by the authors of the mineral description to untypical (not ideally centrosymmetrical) geometry of the davinciite structure. The other quite untypical feature of davinciite is its lavender colour, while the typical eudialyte is rather pink or red.[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. 1 2 3 "Davinciite: Davinciite mineral information and data". Mindat.org. Retrieved 2016-03-08.
  2. 1 2 3 4 5 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.
  3. 1 2 "Davinciite" (PDF). HandbookofMineralogy.org. Retrieved March 1, 2016.


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