Rock & Mineral Encyclopedia

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

Willow Creek Jasper

A prized Idaho jasper known for porcelain-smooth pastel pinks, creams, and greens in soft swirling, orbicular patterns.

Hardened, fine-grained mudrock intermediate between shale and slate, dense and non-fissile, often carved into ornaments.

Dark, organic-rich fine-grained sedimentary rock formed in oxygen-poor waters, often a source rock for oil and gas.

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

A fine-grained sedimentary rock of compacted clay and silt that, unlike shale, breaks in blocks rather than thin layers.

A loose, wind-blown silt deposit, typically buff-colored and very fertile, that forms thick blankets and stands in steep cliffs.

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

A poorly sorted, muddy sandstone with abundant clay matrix between its grains, typically dark and deposited by turbidity currents.

A hard, dark, poorly sorted sandstone with a muddy matrix, typically deposited by underwater turbidity currents.

An opaque brown chalcedony whose iron-stained banding mimics deserts, dunes, and distant mountain skylines.

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

A soft, fine-grained red metamorphosed claystone, sacred to many Native American peoples and carved into ceremonial pipes.

The most common type of mantle peridotite, made of olivine with both orthopyroxene and clinopyroxene, representing fertile upper-mantle rock.

A metamorphic rock made chiefly of manganese-rich spessartine garnet and quartz, formed from ancient manganese-bearing sediments.

An ultramafic intrusive rock made almost entirely of olivine, representing mantle material.