arragonite

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 structureIt 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.