Davinciite
Davinciite is a very rare mineral of the eudialyte group,[2][3] with the simplified formula Na12K3Ca6Fe32+Zr3(Si26O73OH)Cl2.[2][4] The formula given does not show the presence of cyclic silicate groups. The mineral was named after Leonardo da Vinci[4] 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.[3]
| Davinciite | |
|---|---|
| General | |
| Category | Silicate mineral, Cyclosilicate |
| Formula (repeating unit) | Na12K3Ca6Fe2+3Zr3(Si26O73OH)Cl2 (original form) |
| IMA symbol | Dvc[1] |
| 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 | [2][3] |
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.[3]
Notes on chemistry
Impurities in davinciite include strontium, manganese, titanium, with minor aluminium, barium, hafnium, and niobium. Some water is also present.[3]
References
- 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.
- "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. S2CID 97821896.
- "Davinciite" (PDF). HandbookofMineralogy.org. Retrieved March 1, 2016.