Rock & Mineral Encyclopedia

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

Pearl

An organic gem formed inside mollusks from layered nacre, prized for its iridescent luster and classic elegance.

An ultra-high-pressure garnet with silicon in the octahedral site, formed in the deep mantle transition zone and in shocked meteorites.

Phosphate-rich sedimentary rock, the world's main source of phosphorus for fertilizers, formed in nutrient-rich marine settings.

Dark, organic-rich fine-grained sedimentary rock formed in oxygen-poor waters, often a source rock for oil and gas.

A rose-pink manganese silicate marbled with black veins, prized as a tough ornamental and occasionally faceted gemstone.

A depleted mantle peridotite of olivine and orthopyroxene, the refractory residue left after basaltic melt is extracted from the mantle.

A soft, fine-grained red metamorphosed claystone, sacred to many Native American peoples and carved into ceremonial pipes.

An ultramafic intrusive rock made almost entirely of olivine, representing mantle material.

A variety of pyroxenite composed of both orthopyroxene and clinopyroxene with little olivine, found in layered intrusions and the mantle.

A rare ultramafic volcanic rock that erupts from deep in the mantle and is the primary natural source of diamonds.

A chromium-rich magnesium garnet of the pyrope series that crystallizes in the deep mantle and is a valuable diamond indicator mineral.

A rare ultrapotassic, magnesium-rich volcanic rock from deep in the mantle, famous as the diamond host at Argyle in Australia.

Fossil shells whose original material has been replaced by opal, preserving ancient marine forms in common or precious opal.