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
Colour	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 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]

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]

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References

"Davinciite: Davinciite mineral information and data". Mindat.org. Retrieved 2016-03-08.
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.
"Davinciite" (PDF). HandbookofMineralogy.org. Retrieved March 1, 2016.

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[Mindat-1] "Davinciite: Davinciite mineral information and data". Mindat.org. Retrieved 2016-03-08.

[new_K-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.

[HBk-3] "Davinciite" (PDF). HandbookofMineralogy.org. Retrieved March 1, 2016.