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Formula: (Na,Ca)0.3Al2(Si,Al)4O10(OH)2.nH2O
Phyllosilicate (sheet silicate), smectite group, forms series with
saponite and
with montmorillonite
Crystal System: Monoclinic
Specific gravity: 2 to 3 measured
Hardness: 1 to 2
Streak: White
Colour: White, reddish, brownish grey
Common impurities: Ti,K,Mg,Fe
Environments
Pegmatites
Sedimentary environments
Hydrothermal environments
Beidellite is a constituent of bentonitic
clays, an alteration product in hydrothermal mineral deposits, especially
porphyry
copper - molybdenum systems, and
in soils derived from mafic rocks (HOM). It has also been found
in some granitic
pegmatites as "pocket
clay" (Dana). Associated minerals include
plagioclase, quartz,
orthoclase,
montmorillonite,
kaolinite, allophane and
muscovite
(HOM).
Localities
The type locality is Beidell, Crystal Hill Mining District, Saguache County, Colorado, USA.
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