Rock & Mineral Encyclopedia

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

Coal

A combustible black sedimentary rock formed from ancient plant matter and burned for centuries as a primary fossil fuel.

Precious opal from the Andamooka field of South Australia, famous for solid crystal opal and its distinctive treatable matrix opal.

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

A man-made glittering glass colored deep blue with cobalt and studded with tiny copper crystals that mimic a starry night sky.

A porous sedimentary rock naturally saturated with bitumen, dark, tarry-smelling, and historically mined for paving.