Magadiite - Encyclopedia

    Class : Silicates
    Subclass : Tectosilicates
    Crystal system : Monoclinic
    Chemistry : NaSi7O13(OH)3 4H2O
    Rarity : Rare

Magadiite is a curious hydrated sodium silicate that is found in different contexts. Its preferred setting remains recent (post-Pliocene) lacustrine evaporites, where it is deposited from siliceous alkaline (especially sodic) brines. It is found more exceptionally in the marble enclaves of syeno-gabbroic complexes. Its name comes from its location of discovery : Lake Magadi (Kenya). Magadiite forms tiny lamellar crystals, with a sub-orthogonal appearance, agglomerated into spherules then into centimeter-sized beds. Its color is white to pale yellowish-white.

Main photo : Magadiite from Alkali Lake, Oregon, USA © Peter Lof

Magadiite in the World

Its most spectacular deposit is Lake Magadi (its type locality) in the Rift Valley of Kenya, where it was deposited in large beds interstratified with silts, but it has also been identified in the neighboring Lake Bogorio, and Alkali Lake (Oregon), in stringers cutting the saliferous sediments. It was also recognized in Kanem, in the deposits of Lake Chad (Chad). Among its other contexts of formation, note that magadiite is known in the xenolites of the alkaline complex of Mont St-Hilaire (Canada) and in centimeter cavities of the trachytic phonolite of Varennes (Canada).

Right photo : Magadiite from Varennes, Quebec, Canada © Modris Baum

Magadiite in France

Magadiite is not present in the French underground.

Twinning

No twin known for this mineral species.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 2
Density : 2.25
Fracture : Undetermined
Streak : White

TP : Opaque to translucent
RI : 1.470
Birefringence : -
Optical character : Biaxial
Pleochroism : None
Fluorescence : White, blue

Solubility : -

Magnetism : NoneRadioactivity : None

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