Rock & Mineral Encyclopedia

Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.

Chalky Limestone

A soft, fine-grained, porous white limestone made largely of microscopic calcareous plankton skeletons, the rock that forms classic white cliffs.

A porous, spongy freshwater limestone that precipitates around springs, streams and lakes, often encrusting plants and moss.

A porous limestone built from the calcium carbonate skeletons of corals and reef organisms, the lithified remains of ancient or modern reefs.

A soft, porous limestone made of loosely cemented shell and coral fragments, used as a coastal building stone.

A banded, porous limestone deposited by mineral springs, prized as a warm-toned natural building and tile stone.

A porous sedimentary rock naturally saturated with bitumen, dark, tarry-smelling, and historically mined for paving.