Rock & Mineral Encyclopedia

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

Peat

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

A fossiliferous jasper packed with spiral snail shells, technically a silicified gastropod limestone from Wyoming.

A translucent chalcedony decorated with branching, fern-like manganese or iron oxide inclusions resembling tiny plants.

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

A brown fossiliferous chalcedony packed with spiral freshwater snail shells, technically agatized fossil rock from Wyoming.

A common opal containing moss- or fern-like mineral inclusions that resemble plants suspended in a pale silica body.

A porous, spongy freshwater limestone that precipitates around springs, streams and lakes, often encrusting plants and moss.

A fossiliferous limestone built largely from the disc-shaped skeletal plates of crinoids, marine animals known as sea lilies.

A pale jasper threaded with black, fern-like mineral dendrites that mimic plants, trees, and frost despite being inorganic.

A fine-grained clastic rock of silt-sized grains, intermediate between sandstone and mudstone, with a gritty feel.