n. A native carbonate of calcium and magnesium, occurring as a crystallized mineral, and also on a large scale in white granular crystalline rock-masses, and then often called dolomite marble. The proportions of the carbonates vary from 1:1 to 1:3 or 1:5.n. A rock consisting essentially of this mineral.n. a stage of the New York series of formations represented by magnesian limestones, constituting a final phase in the Silurian of the Appalachian region. The formation is characterized by its remarkable profusion of merostome crustaceans of the genera Eurypterus, Pterygotus, Eusarcus, etc., and has commonly been known as the Eurypterus beds, corresponding in position to similar fossiliferous beds of Great Britain and the Baltic provinces.