Magadiite
Magadiite is a hydrous sodium silicate mineral (NaSi7O13(OH)3·4(H2O)) which precipitates from alkali brines as an evaporite phase. It forms as soft (Mohs hardness of 2) white powdery monoclinic crystal masses.[3][4] The mineral is unstable and decomposes during diagenesis leaving a distinctive variety of chert (Magadi-type chert).[7]
| Magadiite | |
|---|---|
 Magadiite. Collected in 1990 from Lake Magadi, Kajiado County, Kenya. | |
| General | |
| Category | Phyllosilicate |
| Formula (repeating unit) | NaSi7O13(OH)3·4(H2O) |
| IMA symbol | Mgd[1] |
| Strunz classification | 9.EA.20 |
| Crystal system | Monoclinic Unknown space group |
| Space group | C2/m (no. 12) |
| Unit cell | a = 7.22 Å, b = 15.70 Å, c = 6.91 Å; β = 97.27°; Z=1 |
| Identification | |
| Color | White |
| Crystal habit | Minute platy crystals; spherulitic aggregates; powdery |
| Tenacity | Puttylike |
| Mohs scale hardness | 2 |
| Luster | Vitreous - dull |
| Streak | White |
| Diaphaneity | Translucent to opaque |
| Specific gravity | 2.25 calculated |
| Optical properties | Biaxial |
| Refractive index | nα = 1.470 |
| Ultraviolet fluorescence | Yellow-white under both long and short wave |
| References | [2][3][4][5][6] |
The mineral was first described by Hans P. Eugster in 1967 for an occurrence in Lake Magadi, Kenya, and is also found at Olduvai Gorge, Tanzania.[4][7] It is also reported from alkalic intrusive syenites as in Mont Saint-Hilaire, Canada.[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.
- Mineralienatlas
- Mineral Handbook
- Webmineral
- Mindat.org
- Garcés, Juan M. (1988). "Hypothetical Structures of Magadiite and Sodium Octosilicate and Structural Relationships Between the Layered Alkali Metal Silicates and the Mordenite- and Pentasil-Group Zeolites1". Clays and Clay Minerals. 36 (5): 409–418. Bibcode:1988CCM....36..409G. doi:10.1346/CCMN.1988.0360505. S2CID 56036567.
- Encyclopedia of Sediments & Sedimentary Rocks, Springer, 2003, p. 417, ISBN 1-4020-0872-4
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.