Sellaite
The importance of Sellaite in our society is undeniable. Whether as a key element in personal development, in the history of humanity, or in the influence on contemporary culture, Sellaite has marked a before and after in various areas. Its relevance has been consolidated over time, making it a topic of constant study and debate. In this article we will explore the many facets of Sellaite, analyzing its impact in different contexts and its evolution throughout history.
| Sellaite | |
|---|---|
 Sellaite crystal from Serra das Éguas, Brazil (size: 4.2 × 2.4 × 2 cm) | |
| General | |
| Category | Halide mineral |
| Formula | MgF2 |
| IMA symbol | Sel[1] |
| Strunz classification | 3.AB.15 |
| Crystal system | Tetragonal |
| Crystal class | Ditetragonal dipyramidal (4/mmm) H-M symbol: (4/m 2/m 2/m) |
| Space group | P42/mnm |
| Unit cell | a = 4.6213(2) Å c = 3.0519(1) Å Z = 2 |
| Identification | |
| Color | Colorless to white |
| Crystal habit | Prismatic crystals; fibrous, radial, spherulitic |
| Twinning | On {011} |
| Cleavage | Perfect on {010} and {110} |
| Fracture | Conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 5–5.5 |
| Luster | Vitreous |
| Diaphaneity | Transparent |
| Specific gravity | 3.15 |
| Optical properties | Uniaxial (+) |
| Refractive index | nω = 1.378 nε = 1.390 |
| Birefringence | δ = 0.012 |
| References | [2][3][4] |
Sellaite is a magnesium fluoride mineral with the formula MgF2. It crystallizes in the tetragonal crystal system, typically as clear to white vitreous prisms. It may be fibrous and occur as radiating aggregates. It has a Mohs hardness of 5 to 6 and a specific gravity of 2.97 to 3.15. Refractive index values are nω = 1.378 and nε = 1.390.
Discovery and occurrence
Sellaite was first described in 1868 and named for Italian mining engineer and mineralogist Quintino Sella (1827–1884). Its type locality is the glacier de Gébroulaz in France, where it occurred inside bitumen-bearing dolomite-anhydrite clasts within a moraine deposit. It has been reported in an evaporite deposit at Bleicherode; within volcanic ejecta and fumaroles at Vesuvius; in a metamorphic magnesite deposit at Serra das Éguas; and in sodic alkali granite near Gjerdingen.[2][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.
- ^ a b Mineral Data Publishing: Handbook of Mineralogy
- ^ a b Mindat with location data.
- ^ Webmineral data.
- Palache, C., H. Berman, and C. Frondel (1951) Dana’s system of mineralogy, (7th edition), v. II, pp. 37–39