Rock & Mineral Encyclopedia

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

Tuff

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

A rare moonstone that shows a four-rayed star of light (asterism) across its domed surface along with adularescence.

A copper-iron sulfide ore famous for its iridescent peacock-like purple and blue tarnish; often sold as treated chalcopyrite.

A dark gray-to-black feldspar variety of moonstone that shows blue and white adularescent flash against a smoky body.

A plagioclase feldspar famous for labradorescence, a dramatic flash of iridescent blue, green, and gold across a dark gray stone.

A single beryl crystal showing two distinct color zones, such as aquamarine blue grading into morganite pink, within one stone.

The rarest and most valuable opal, with a dark body tone that makes its flashing rainbow play-of-color blaze brilliantly.

A trade name for lightly saturated elbaite tourmalines in delicate pastel pinks, mints, peaches, and blues popular in modern jewelry.

A frothy, lightweight volcanic glass so full of gas bubbles that it can float on water.

A hydrated volcanic glass with pearly, onion-like concentric cracks that pops into lightweight white granules when heated.

A lightweight black organic gemstone formed from fossilized wood under pressure, a type of lignite long used in mourning jewelry.

Fossilized tree resin, warm and lightweight, sometimes preserving ancient insects and plant matter inside.

A soft, lightweight siliceous sedimentary rock made of fossil diatom remains, prized as a fine natural abrasive and polishing powder.