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Related to infusorial earth: diatomaceous earth
infusorial earth[‚in·fyə′sȯr·ē·əl ′ərth]
Formerly, and incorrectly, a soft rock or an earthy substance composed of siliceous remains of diatoms.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.