Rock & Mineral Encyclopedia

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

Crinoidal Limestone

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

Calcium-carbonate sedimentary rock packed with visible fossils, recording ancient marine life within an easily scratched, fizzing matrix.

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

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

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

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

Coarse, clear-to-white crystalline calcite that cements limestones, contrasting with fine muddy micrite.

A soft, earthy sedimentary rock made of a mixture of calcium carbonate and clay, intermediate between limestone and mudstone.

A very fine-grained, mud-sized limestone formed from carbonate mud, smooth and dense with conchoidal fracture.

A fractured fine-grained limestone whose iron-stained crack networks form natural scenes resembling ruined cities and landscapes.

A marbled, abstractly patterned stone resembling modern art, technically a metamorphosed limestone rather than a true silica jasper.

Quartz with a wider crystal 'cap' that grew over a narrower stem, forming a natural scepter or mushroom shape.

A rounded sedimentary nodule cracked internally and filled with veins of yellow calcite, prized for its striking dragon-skin patterning.