Rock & Mineral Encyclopedia

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

Lake Michigan Agate

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

Rhyolite that has been metamorphosed, recrystallizing its silica-rich volcanic material into a tougher felsic metamorphic rock.

An Australian green rhyolite with eye-like orbs and earthy patterns marketed as jasper, evoking dense rainforest foliage.

A vivid yellow-and-black banded stone from Indonesian volcanic vents, colored by sulfur, arsenic minerals and iron oxides, not true jasper.

A banded rhyolitic volcanic rock with swirling tan, red, and yellow iron-oxide layers prized as a decorative picture stone.

A rare ultrapotassic, magnesium-rich volcanic rock from deep in the mantle, famous as the diamond host at Argyle in Australia.

A soft, green, foliated rock rich in chlorite, formed by low-grade metamorphism of mafic or volcanic rocks.

Rare precious opal from Tintenbar in northern New South Wales, Australia, occurring in volcanic basalt rather than sedimentary rock.

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

A dull, resinous volcanic glass similar to obsidian but with higher water content and a waxy pitch-like luster.

Fine, golden, hair-like strands of basaltic volcanic glass spun from fluid lava droplets during eruptions, named for the Hawaiian volcano goddess.

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

Black volcanic glass laced with delicate web-like veins of contrasting color, formed by flow banding and fine crystallization.

A common coarse-grained intrusive rock like granite but richer in plagioclase than potassium feldspar.