Beidellite, (Na,Ca0.5)0.3Al2(Si,Al)4O10(OH)2nH2O, is a white, reddish, or brownish-gray monoclinic clay mineral of the smectite group. — Photo: Nessa Eull · CC0
Beidellite
Beidellite is an IMA-recognized mineral species in the silicate class, with the chemical formula (Na,Ca)₀.₃Al₂(Si,Al)₄O₁₀(OH)₂·nH₂O.
It is a member of the Clay, Smectite-vermiculite structural group.
Key properties: Mohs hardness 1–2; specific gravity 2–3; typically white or yellow or brown or gray; white streak; Waxy to vitreous luster; optically biaxial.
IMA symbol Bei, grandfathered status — known before the IMA’s founding, named in 1925.
A constituent of bentonitic clays; an alteration product in hydrothermal mineral deposits, especially porphyry Cu-Mo systems; in soils derived from mafic rocks.
It is found associated with Plagioclase, quartz, orthoclase, montmorillonite, kaolin, allophane, muscovite.
The name refers to Beidell, Colorado, USA.
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