Rock & Mineral Encyclopedia

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

Chalk

A soft, white, fine-grained limestone made almost entirely of microscopic marine plankton skeletons.

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

A soft carbonate sedimentary rock made mostly of calcite, often packed with marine fossils and prone to forming caves.

The softest mineral on the Mohs scale, talc has a greasy, soapy feel and is the source of talcum powder and soapstone.

A magnesium carbonate mineral, usually chalky white with grey veining, widely dyed to imitate turquoise and other stones.

A soft, lightweight, chalky sedimentary rock made of the silica shells of microscopic diatoms, prized for its absorbency and filtering ability.