Rock & Mineral Encyclopedia

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

Tourmaline

A boron-rich silicate gemstone group famous for occurring in every color of the rainbow, sometimes several within a single crystal.

An intermediate plutonic rock with nearly equal alkali and plagioclase feldspar and very little quartz, sitting between diorite and syenite.

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

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

A dark, foliated schist rich in graphite that leaves a grey-black mark and forms from metamorphosed carbon-rich sediments.

A pale chalcedony agate with cloudy, frost-like white patterning suggesting frost on a window or icy crystalline textures.

A tourmaline displaying two or more distinct colors in a single crystal, prized for natural color zoning like watermelon and bicolor stones.