Magadiite

Magadiite
General
Category Phyllosilicate
Formula
(repeating unit)
NaSi7O13(OH)3·4(H2O)
Strunz classification 09.EA.20
Unit cell a = 7.25 Å, b = 7.25 Å, c = 15.69 Å; β = 96.8°; Z=2
Identification
Color White
Crystal habit Minute platy crystals; spherulitic aggregates; powdery
Crystal system Monoclinic
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 [1][2][3]

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.[1][2] The mineral is unstable and decomposes during diagenesis leaving a distinctive variety of chert (Magadi-type chert).[4]

The mineral was first described by Hans P. Eugster in 1967 for an occurrence in Lake Magadi, Olduvai Gorge, Kenya.[2][4] It is also reported from alkalic intrusive syenites as in Mont Saint-Hilaire, Canada.[1]

References


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