Rock & Mineral Encyclopedia

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

Silcrete

Extremely hard surface rock formed when silica cements soil and sediment into a tough duricrust in arid landscapes.

The highest-rank coal, a hard, lustrous black rock that burns cleanly with little smoke and high heat output.

A brown fossiliferous chalcedony packed with spiral freshwater snail shells, technically agatized fossil rock from Wyoming.

A pegmatite rock of feldspar intergrown with wedge-shaped quartz that resembles ancient runic or Hebrew writing.

Ancient chemically deposited rock of alternating iron-oxide and silica bands recording Earth's early oxygenation and a major iron ore source.

A banded combination rock of golden tiger's eye, red jasper, and metallic hematite, formed in ancient iron deposits.

A green ornamental stone, often serpentine-rich marble or verde antique, valued for its rich green color and white veining.

Smithsonite is a zinc carbonate ore famous for glassy botryoidal crusts in blue-green, pink, and yellow hues.

A hard aluminum borosilicate famous for its rich denim-blue color, often forming dense fibrous masses or coloring quartz blue.

A blue calcium phosphate mineral with vivid color and middling hardness, the same mineral family that forms bones and teeth.