Rock & Mineral Encyclopedia

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

Tripolite

A soft, lightweight siliceous sedimentary rock made of fossil diatom remains, prized as a fine natural abrasive and polishing powder.

Soft, lightweight siliceous rock made of fossilized diatom shells, valued as a filter, abrasive, and absorbent.

The hardest known natural material, a crystalline form of pure carbon prized as the ultimate gemstone for its brilliance and fire.

Small ironstone concretions from Yowah, Queensland, whose hollow or veined centers hold brilliant precious boulder opal.

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.

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