Rock & Mineral Encyclopedia

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

Pumice

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

Natural obsidian with a frosted, matte surface produced by weathering, abrasion, or etching rather than a separate variety of glass.

The gem variety of cordierite, famous for strong pleochroism that shifts from violet-blue to near-colorless.

A pink-and-green bicolor glass sold as obsidian; the watermelon coloring is manufactured and does not occur in natural volcanic glass.

Tourmaline crystals displaying two or more distinct colors at once, including the famous pink-and-green watermelon variety.