| Magadiite | |
| Category: | Phyllosilicate |
| Formula: | NaSi7O13(OH)3·4(H2O) |
| Imasymbol: | Mgd[1] |
| Strunz: | 9.EA.20 |
| Symmetry: | C2/m (no. 12) |
| Unit Cell: | a = 7.22 Å, b = 15.70 Å, c = 6.91 Å; β = 97.27°; Z=1 |
| Color: | White |
| Habit: | Minute platy crystals; spherulitic aggregates; powdery |
| System: | Monoclinic Unknown space group |
| Tenacity: | Puttylike |
| Mohs: | 2 |
| Luster: | Vitreous - dull |
| Streak: | White |
| Diaphaneity: | Translucent to opaque |
| Gravity: | 2.25 calculated |
| Opticalprop: | Biaxial |
| Refractive: | nα = 1.470 |
| Fluorescence: | Yellow-white under both long and short wave |
| References: | [2] [3] [4] |
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.[5] [6] The mineral is unstable and decomposes during diagenesis leaving a distinctive variety of chert (Magadi-type chert).[7]
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.[6] [7] It is also reported from alkalic intrusive syenites as in Mont Saint-Hilaire, Canada.[5]