dolomite /(dŏl"ō̇*mīt)/

dol·o·mite

dolomite

n.
  1. 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. (Geol. & Min.)