bentonite
BEN-toh-nite
A highly absorbent, swelling clay formed from the weathering of volcanic ash. Bentonite can absorb several times its weight in water, expanding dramatically and becoming slippery, plastic, and nearly impervious. Wet bentonite on a trail or road is one of the most treacherous walking and driving surfaces in the West — it clings to boots in heavy, accumulating slabs and turns roads into impassable grease. Dry, it cracks into a mosaic of hard, pale flakes. The badlands of the Northern Plains and the desert hills of the Colorado Plateau are rich in it.
Etymology
Named for Fort Benton, Montana, near the location where it was first described in 1898. The clay is associated with Cretaceous-era volcanic ash deposits across the Western Interior.
Notes
Anyone who has hiked in the Badlands of South Dakota or the Bisti Wilderness of New Mexico after a rain knows bentonite in their bones — and on their boots.
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