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 coarse sedimentary rock of rounded pebbles and gravel cemented in a finer matrix, recording ancient rivers and beaches.

A conglomerate altered by heat and pressure, often with its rounded pebbles stretched and flattened into elongated lenses.

Rounded nodules of translucent obsidian, named after a Native American legend, that glow smoky brown when held to light.

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