a valuable clay, formed by the decomposition of volcanic ash, that swells as it absorbs water: used as a filler in the building, paper, and pharmaceutical industries
Word origin
C19: from Fort Benton, Montana, USA, where found, + -ite1
bentonite in American English
(ˈbɛntənˌaɪt)
US
noun
a porous clay consisting mainly of the mineral montmorillonite, which swells greatly when it absorbs water
Word origin
after Fort Benton (named for Senator Benton: see Benton) in Montana, where it is found