Rock & Mineral Encyclopedia

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

Dryhead Agate

A banded fortification agate from the remote Dryhead area of south-central Montana, prized for warm concentric rings.

A vividly banded fortification agate from Argentina prized for its bold red, gold and white concentric patterns.

The state gemstone of South Dakota, a rare fortification agate known for tight, holly-leaf concentric banding.

A fortification agate from the Black Hills of South Dakota, known for tight, colorful banding closely related to the famous Fairburn agate.

A black-and-white striped chalcedony-quartz rock whose bold zebra-like banding makes it a popular ornamental and lapidary stone.