Rock & Mineral Encyclopedia

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

Sardonyx

A banded chalcedony combining reddish-brown sard with white or black onyx layers, prized since antiquity for carved cameos.

A green-and-white banded metamorphic marble whose wavy mica layers resemble the rings of a sliced onion.

Boulder opal from the Koroit field in Queensland, famous for intricate ironstone matrix patterns laced with colorful precious opal.

Precious opal that forms in thin veins within brown ironstone boulders, cut with the host rock left as a natural dark backing.

An intensely glowing copper-bearing tourmaline whose electric neon-blue color makes it one of the most valuable gems in the world.

Boulder opal from the Quilpie district of Queensland, Australia, with bright color set in dark ironstone matrix.

Opal from Lightning Ridge, Australia, the world's premier source of black opal with brilliant color on a dark body.

A hydrated volcanic glass with pearly, onion-like concentric cracks that pops into lightweight white granules when heated.

A single beryl crystal showing two distinct color zones, such as aquamarine blue grading into morganite pink, within one stone.

A limestone packed with visible shells and shell fragments, recording the accumulation of marine invertebrate remains on ancient sea floors.