Rock & Mineral Encyclopedia

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

Coquina

A soft, porous limestone made of loosely cemented shell and coral fragments, used as a coastal building stone.

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

A pale translucent chalcedony threaded with brown-black manganese and iron dendrites that mimic tiny ferns, mosses or landscapes.

Rounded nodules of translucent obsidian, named after a Native American legend, that glow smoky brown when held to light.

Sand-grained limestone composed of carbonate particles such as shell fragments and ooids cemented into a calcite rock.

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

Glacially deposited banded agates found along Lake Michigan beaches, small waterworn pebbles with concentric red and grey banding.

Glacially transported banded agates found along Lake Huron's shores, typically small, frosted pebbles with red-orange iron banding.

A jasper made of angular fragments naturally cemented back together, typically showing red and brown pieces in a quartz matrix.