Rock & Mineral Encyclopedia

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

Oolitic Limestone

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

A hard, fine-grained siliceous rock built from the microscopic silica skeletons of radiolarians, often forming colorful ribbon-banded cherts.

A rounded sedimentary nodule cracked internally and filled with veins of yellow calcite, prized for its striking dragon-skin patterning.

A fossiliferous jasper packed with spiral snail shells, technically a silicified gastropod limestone from Wyoming.