Rock & Mineral Encyclopedia

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

Calcrete

Carbonate-cemented soil crust formed in arid regions where calcium carbonate accumulates and hardens within the regolith.

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

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

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

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

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

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

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

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

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

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.