Rock & Mineral Encyclopedia

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

Oolitic Limestone

Limestone built from tiny rounded ooid grains resembling fish roe, formed in warm, agitated shallow seas.

A coarse sedimentary rock of rounded pebbles and gravel cemented in a finer matrix, recording ancient rivers and beaches.

A conglomerate altered by heat and pressure, often with its rounded pebbles stretched and flattened into elongated lenses.

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.

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

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

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

A jasper marked with soft feather- or plume-like mineral inclusions that drift through a pale silica body.

A pale chalcedony agate with cloudy, frost-like white patterning suggesting frost on a window or icy crystalline textures.

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

A finely speckled pale jasper trade stone named for its sesame-seed-like flecks, closely related to Kiwi Jasper.

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