Normandite
| Normandite | |
|---|---|
 | |
| General | |
| Category | Minerals |
| Formula | NaCa(Mn2+,Fe2+)(Ti,Nb,Zr)Si2O7(O,F)2 |
| IMA symbol | Nmd[1] |
| Crystal system | Monoclinic |
| Space group | P21/a (no. 14) |
| Identification | |
| Mohs scale hardness | 5 - 6 |
| Specific gravity | 3.48 - 3.5 |
| References | [2] |
Normandite is an orange-brown, monoclinic sorosilicate mineral with the idealised formula NaCa(Mn,Fe)(Ti,Nb,Zr)Si2O7OF. It is the titanium analogue of låvenite and a member of the wöhlerite group.[3][4]
History
[edit]Charles Normand discovered the mineral in 1980 at the Poudrette quarry, Mont-Saint-Hilaire, Quebec. George Y. Chao and Robert A. Gault described it as a new mineral species in 1997 and named it in Normand's honour.[3]
Occurrence and properties
[edit]The Poudrette quarry is the type locality. There, normandite occurs in nepheline syenite and its miarolitic cavities, associated with nepheline, albite, microcline, aegirine, natrolite, catapleiite, kupletskite, eudialyte, cancrinite, villiaumite, rinkite and donnayite-(Y). It forms transparent to translucent orange-brown aggregates of subparallel acicular crystals up to 10 mm (0.39 in) long, as well as yellow fibrous patches.[3]
The mineral has a white to very pale-yellow streak, a vitreous lustre, distinct {100} and {001} cleavages, and a conchoidal fracture. Its Mohs hardness is 5–6 and its measured density is about 3.50 g/cm3.[3]
Classification and structure
[edit]Normandite crystallises in space group P21/a. Its structure has the four-column-wide walls of cation-centred polyhedra characteristic of wöhlerite-group minerals, interconnected by corner sharing and by Si2O7 groups. Its relationship to låvenite principally reflects substitution of Ti for Zr in corresponding structural sites.[4]
References
[edit]- ↑ 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.
- ↑ Perchiazzi, N.; McDonald, A. M.; Gault, R. A.; Johnsen, O.; Merlino, S. (1 June 2000). "The Crystal Structure of Normandite and Its Crystal-Chemical Relationships With Lavenite". The Canadian Mineralogist. 38 (3): 641–648. Bibcode:2000CaMin..38..641P. doi:10.2113/gscanmin.38.3.641.
- 1 2 3 4 Chao, George Y.; Gault, Robert A. (1997). "Normandite, the Ti-analogue of låvenite from Mont Saint-Hilaire, Quebec". The Canadian Mineralogist. 35: 1035–1039.
- 1 2 Dal Bo, Fabrice; Friis, Henrik; Mills, Stuart J. (2022). "Nomenclature of wöhlerite-group minerals". Mineralogical Magazine. 86 (4): 661–676. doi:10.1180/mgm.2022.10. hdl:10852/95029.