Rock & Mineral Encyclopedia

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

Menilite Opal

An opaque grey-brown common opal forming nodules and concretions, historically called liver opal for its dull brownish color.

Tourmaline crystals displaying two or more distinct colors at once, including the famous pink-and-green watermelon variety.

A fine-grained, silica-rich volcanic rock that is the extrusive equivalent of granite, often pale, banded, or flow-textured.

A hard, fine-grained sedimentary silica rock that breaks with sharp conchoidal edges, prized by ancient toolmakers.

A warm orange-to-red variety of chalcedony quartz colored by iron oxide, used since antiquity for seals, beads, and cabochons.

An altered granite mottled pink and green from feldspar and epidote, popular as a tough, colorful ornamental rock.

A solid jet-black chalcedony, usually a dyed and treated agate, prized for sleek polished beads, cabochons, and intaglios.

A banded combination rock of golden tiger's eye, red jasper, and metallic hematite, formed in ancient iron deposits.

A banded variety of chalcedony quartz, classically black or black-and-white, long favored for cameos and beads.

A translucent, soft blue variety of microcrystalline quartz whose color comes from light scattering through its fine structure.