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 fossiliferous limestone built largely from the disc-shaped skeletal plates of crinoids, marine animals known as sea lilies.

A patterned jasper whose scaly, net-like markings recall reptile skin, popular with lapidaries for its organic camouflage look.

A green-and-black mottled jasper whose scale-like patterning resembles reptile skin, often linked to Kambaba and crocodile jaspers.

An opaque patterned jasper named for its scaly, snakeskin-like surface markings of interlocking tan and brown cells.

Tabular quartz crossed by a milky white thread-like line marking where the crystal repeatedly cracked and re-healed.