Rock & Mineral Encyclopedia

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

Flint

A hard, dark variety of chert that knaps into razor-sharp edges and sparks against steel, central to Stone Age technology.

Quartz containing a sealed pocket of ancient water, often with a mobile air bubble that moves when the crystal is tilted.

A reddish-brown rare-earth phosphate that is a primary ore of cerium, thorium and other rare-earth elements, often found in placer sands.

Tourmaline showing many color zones in a single crystal, often revealing spectacular concentric patterns when sliced.

A man-made opalescent glass that glows milky blue in reflected light and warm orange when backlit, often sold as a crystal.