Rock & Mineral Encyclopedia

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

Dacite

A fine-grained volcanic rock intermediate between andesite and rhyolite, common at explosive stratovolcanoes.

A high-grade metamorphic gneiss of garnet, sillimanite, quartz, and graphite, derived from ancient aluminous sediments.

The most common sedimentary rock, a fissile mudrock of compacted clay and silt that splits into thin layers.

A banded agate that displays a moving shadow or flash across its surface when tilted under light, caused by closely spaced parallel bands.

A prized Idaho picture jasper from Bruneau Canyon known for brown and cream orbicular egg-rock patterns and scenic landscapes.

A cream-colored spotted stone resembling a Dalmatian dog, made of feldspar and quartz dotted with dark mineral grains.

The official state rock of Kentucky, a banded agate famous for striking deep-red and black fortification patterns.

An altered granite mottled pink and green from feldspar and epidote, popular as a tough, colorful ornamental rock.

A cream-colored feldspar-and-quartz rock peppered with dark spots, named for its resemblance to a Dalmatian dog.

A hard, tough metamorphic rock of fused quartz grains, formed by recrystallizing quartz sandstone under heat and pressure.

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

A fine-grained, low-grade metamorphic rock that splits into flat sheets along slaty cleavage, long used for roofing and flooring.

A banded, metamorphosed iron formation in which bright red jasper alternates with silvery hematite or magnetite layers.

A foliated metamorphic rock of calcite mixed with mica, quartz, and calc-silicate minerals, derived from marly sediments.

Agate that forms in flat cracks or veins of host rock rather than rounded nodules, producing straight, parallel banding.