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A mineral identical in composition with calcite or carbonate of lime, but differing from it in its crystalline form and some of its physical characters.

related to muscovite, but containing soda instead of potash. It is characteristic of the paragonite schist of the Alps.

ubstance having such forms; -- as, carbonate of lime occurs in the allomorphs calcite and aragonite.

See Aragonite.

carbonate of lime. It is rhombohedral in its crystallization, and thus distinguished from aragonite. It includes common limestone, chalk, and marble. Called also calc-spar and calcareous spar.

Either one of the two forms of a dimorphous substance; as, calcite and aragonite are dimorphs.

o independent forms of the same chemical compound, as of calcium carbonate as calcite and aragonite.

A variety of aragonite, occuring in delicate white coralloidal forms; -- common in beds of iron ore.

-- called also aikinite. -- Needle shell (Zoöl.), a sea urchin. -- Needle spar (Min.), aragonite. -- Needle telegraph, a telegraph in which the signals are given by the deflections of a magnetic needle to the right or to the left of a certain position. -- Sea needle (Zoöl.), the garfish.

hange of physical characters without alteration of chemical composition, as the change of aragonite to calcite.

s of a system other than that to which they belong, as the apparently hexagonal prisms of aragonite.