Rock & Mineral Encyclopedia

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

Coquina

A soft, porous limestone made of loosely cemented shell and coral fragments, used as a coastal building stone.

Translucent banded calcium-carbonate stone deposited in caves and springs, prized for ornamental carvings despite its softness.

Extremely fine-grained, even-textured limestone famous for lithographic printing and for preserving exquisite fossils like Archaeopteryx.

A chemical deposit precipitated around hot springs and geysers, either siliceous (geyserite) or calcareous, forming delicate terraces and crusts.

Calcium-carbonate sedimentary rock packed with visible fossils, recording ancient marine life within an easily scratched, fizzing matrix.

Limestone built from tiny rounded ooid grains resembling fish roe, formed in warm, agitated shallow seas.

A metamorphosed limestone of interlocking calcite crystals, prized for sculpture and architecture for its workability and polish.

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

A soft, earthy sedimentary rock made of a mixture of calcium carbonate and clay, intermediate between limestone and mudstone.

A rare igneous rock made mostly of carbonate minerals, source of the world's most important rare-earth-element and niobium deposits.

Siderite is an iron carbonate ore, a brown rhombohedral mineral of the calcite group found in sediments and veins.