A soft, earthy, fine-textured, usually white to light-gray or buff limestone of marine origin. It consists almost wholly (90% to 99%) of calcite, formed mainly by shallowwater accumulation of calcareous remains of floating microorganisms (chiefly foraminifers) and of comminuted remains of calcareous algae, set in a structureless matrix of very finely crystalline calcite. The rock is porous, somewhat friable, and only slightly coherent.