Images
Formula: Na2Si14O28(OH)2.8H2O
Hydrated phyllosilicate (sheet silicate)
Crystal System: Orthorhombic
Specific gravity: 2.25 calculated
Hardness: 2
Streak: White
Colour: White
Luminescence: Yellow-white fluorescence under both long wave and short wave UV
Solubility: Magadiite in dilute acid at room temperature produces a hydrous form of silica. Subsequent
treatment of the silica with concentrated solutions of Na2CO3 or NaOH produces
magadiite again
(Mindat).
Common impurities: Ti,Al,Fe,Mn,Mg,Ca,K
Environments
Magadiite is unstable and decomposes during diagenesis leaving a distinctive variety of
chert
(Wiki).
Magadiite is associated with other rare alkalic minerals in brines with high Ph (alkaline) and silica content
(WebMin).
Localities
At the Poudrette quarry, Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Québec, Canada, magadiite
occurs in marble xenoliths in an intrusive alkalic
gabbro-syenite complex.
Associated minerals include bavenite,
pectolite, apophyllite,
phlogopite, quartz and
thaumasite
(HOM).
Magadiite from the Poudrette Quarry -
Image
At the Saint-Amable sill, Varennes & St-Amable, Lajemmerais RCM, Montérégie, Québec, Canada, magadiite
occurs in miarolitic cavities in the nepheline syenite sill
near Saint-Amable. Associated minerals include varennesite,
natrolite, eudialyte,
shkatulkalite, makatite,
pectolite, sphalerite,
monazite-(Ce), serandite,
zakharovite, lorenzenite,
aegirine and
tuperssuatsiaite
(HOM).
Magadiite from the Saint-Amable sill -
Image
At the Lac Region, Chad, magadiite occurs associated with kanemite
(HOM).
Magadiite from Chad - Image
At the type locality, Lake Magadi, Kajiado County, Kenya, magadiite occurs in silts precipitated by
evaporation of saline brines, and associated with kenyaite
and calcite
(HOM).
It is found as white putty-like laminae, in beds varying in thickness from 5 cm to 60 cm
(Mindat).
Magadiite from Lake Magadi - Image
About 5 km north of Trinity Lake, Trinity County, California. USA, magadiite occurs in altered volcanic rocks
(HOM).
At Alkali Lake, Lake County, Oregon, USA, magadiite occurs in veins cutting playa sediments and in muds
associated with alkali salts and brines
(HOM).
Magadiite from Alkali Lake -
Image
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