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Magadiite

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Magadiite
Magadiite. Collected in 1990 from Lake Magadi, Kajiado County, Kenya.
General
CategoryPhyllosilicate
Formula
(repeating unit)
NaSi7O13(OH)3·4(H2O)
IMA symbolMgd[1]
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[2][3][4][5][6]

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]

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

[edit]
  1. ^ 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.
  2. ^ Mineralienatlas
  3. ^ a b c Mineral Handbook
  4. ^ a b c Webmineral
  5. ^ Mindat.org
  6. ^ 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.
  7. ^ a b Encyclopedia of Sediments & Sedimentary Rocks, Springer, 2003, p. 417, ISBN 1-4020-0872-4