In mineralogy, a species of carbonate of lime, but not pure, and said to contain 3 or 4 per cent. of carbonate of strontian. It differs from pure carbonate of lime, in hardness, specific gravity, crystaline structure, &c. It is harder than calcarious spar, and exhibits several varieties of structure and form. It is often crystallized, generally in hexahedral prisms or pyramids. The massive varieties have usually a fibrous structure, exhibiting various imitative forms, being sometimes coraloidal.