Rock & Mineral Encyclopedia

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

Multicolor Tourmaline

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

Obsidian with a vivid blue sheen or hue; natural blue obsidian is rare, and intensely uniform blue material is usually manufactured glass.

Black volcanic glass that flashes a green sheen at certain angles due to light interference off aligned microscopic inclusions.

Clear quartz mined in the Himalayan region, often double-terminated and containing dark hematite or carbon inclusions.

Iron-stained sandstone whose red color comes from hematite coatings, formed in oxidizing desert, river, and coastal environments.

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

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

The lithium-rich tourmaline species responsible for nearly all gem tourmaline, occurring in every color of the rainbow.

Precious opal with a warm chocolate-brown body tone that makes its rainbow play-of-color glow, mainly from Ethiopia and Mexico.

Australia's classic light-bodied precious opal from Coober Pedy, famed for milky white stones flashing pastel rainbow play-of-color.

A magnesium carbonate mineral, usually chalky white with grey veining, widely dyed to imitate turquoise and other stones.

A rare dark ultramafic alkaline igneous rock built mostly of titanaugite and magnetite, named for Jacupiranga in Brazil.

A natural sheen obsidian combining a bright silver shimmer with iridescent peacock colors, all produced by nanoparticle layers in black glass.

A natural sheen obsidian showing a warm gold shimmer plus peacock iridescence, caused by aligned nanoparticle layers within black glass.

A rare zirconium-bearing garnet that crystallizes in carbonatites and alkaline rocks, first described from Magnet Cove, Arkansas.