Rock & Mineral Encyclopedia

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

Opalized Wood

Fossilized wood in which the original organic structure has been replaced by opal, sometimes showing precious play-of-color.

Sand-grained limestone composed of carbonate particles such as shell fragments and ooids cemented into a calcite rock.

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