Rock & Mineral Encyclopedia

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

Bituminous Coal

A dense, black, mid-rank coal with high energy content, widely used for power generation and to make coke for steelmaking.

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

A mottled, multicolored obsidian blending black, brown, grey, and tan patches like a calico cat's patchwork coat.

A South African quartz whose central crystal is coated in a cactus-like crust of tiny secondary points, also called spirit quartz.