Rock & Mineral Encyclopedia

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

Emerald in Matrix

Natural emerald crystals still embedded in their host rock, prized as mineral specimens that show how the gem grew in place.

Rounded nodules of translucent obsidian, named after a Native American legend, that glow smoky brown when held to light.

A rare boron-bearing feldspar, the boron analogue of albite, first found in oil-shale nodules of the Green River Formation.

An opaque grey-brown common opal forming nodules and concretions, historically called liver opal for its dull brownish color.