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negative crystal[′neg·əd·iv ′krist·əl]
A crystal containing a cavity, where the form of the cavity is one of the characteristic crystal forms of the mineral in question.
A uniaxial crystal in which the extraordinary wave travels faster than the ordinary wave, such as calcite.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.