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.[2][3] The mineral is unstable and decomposes during diagenesis leaving a distinctive variety of chert (Magadi-type chert).[6]

Magadiite
Magadiite-696064.jpg
Magadiite. Collected in 1990 from Lake Magadi, Kajiado County, Kenya.
General
CategoryPhyllosilicate
Formula
(repeating unit)		NaSi7O13(OH)3·4(H2O)
Strunz classification9.EA.20
Crystal systemMonoclinic
Unknown space group
Space groupC2/m (no. 12)
Unit cella = 7.22 Å, b = 15.70 Å,
c = 6.91 Å; β = 97.27°; Z=1
Identification
ColorWhite
Crystal habitMinute platy crystals; spherulitic aggregates; powdery
TenacityPuttylike
Mohs scale hardness2
LusterVitreous - dull
StreakWhite
DiaphaneityTranslucent to opaque
Specific gravity2.25 calculated
Optical propertiesBiaxial
Refractive indexnα = 1.470
Ultraviolet fluorescenceYellow-white under both long and short wave
References[1][2][3][4][5]

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.[3][6] It is also reported from alkalic intrusive syenites as in Mont Saint-Hilaire, Canada.[2]

This article uses material from the Wikipedia article
 Metasyntactic variable, which is released under the 
Creative Commons
Attribution-ShareAlike 3.0 Unported License

Note

This article uses material from the Wikipedia article
 Metasyntactic variable, which is released under the 
Creative Commons
Attribution-ShareAlike 3.0 Unported License.