Rock & Mineral Encyclopedia

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

Mushroom Tourmaline

A rare mushroom-shaped tourmaline growth habit, typically magnesium-rich dravite/uvite, prized by collectors for its fungus-like cap-and-stem form.

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

A soft, lightweight siliceous sedimentary rock made of fossil diatom remains, prized as a fine natural abrasive and polishing powder.

Extremely fine-grained, even-textured limestone famous for lithographic printing and for preserving exquisite fossils like Archaeopteryx.

A soft carbonate sedimentary rock made mostly of calcite, often packed with marine fossils and prone to forming caves.

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

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.