Bit·ter spar A common name of dolomite; -- so called because it contains magnesia, the soluble salts of which are bitter. See Dolomite.
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dol·o·mite n. Geol. & Min. A mineral consisting of the carbonate of lime and magnesia in varying proportions. It occurs in distinct crystals, and in extensive beds as a compact limestone, often crystalline granular, either white or clouded. It includes much of the common white marble. Also called bitter spar.
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