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smectite

SEM of authigenic quartz and smectite
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1. n. [Geology]
[(1/2Ca,Na)0.7(Al,Mg,Fe)4(Si,Al)8O20(OH)47nH2O)]

A group of clay minerals that includes montmorillonite. This type of mineral tends to swell when exposed to water. Bentonite includes minerals of the smectite group.