Rock & Mineral Encyclopedia

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

Conglomerate

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 light, porous volcanic rock formed from compacted and cemented ash erupted during explosive eruptions.

A porous sedimentary rock naturally saturated with bitumen, dark, tarry-smelling, and historically mined for paving.

A general term for light-colored, fine-grained volcanic rocks rich in quartz and feldspar, like rhyolite.