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 black iron-manganese niobate that is a primary ore of niobium, forming a continuous series with tantalite (together called coltan).

A dense black iron-manganese tantalate that is the chief ore of tantalum, forming a series with columbite and mined as coltan.

Quartz with a stepped, multi-pointed structure of parallel side crystals resembling the spires of a cathedral.

A limestone packed with visible shells and shell fragments, recording the accumulation of marine invertebrate remains on ancient sea floors.

A soft, spongy accumulation of partly decayed plant matter that forms in waterlogged bogs and is the first step toward coal.

A dark green-and-black stromatolite jasper patterned with swirling orbs, formed from fossilized ancient microbial colonies.