Rock & Mineral Encyclopedia

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

Basalt

A fine-grained, dark volcanic rock that erupts as fluid lava and forms most of the ocean floor and many lava plateaus.

A dark, highly vesicular volcanic rock full of gas bubbles, denser than pumice, common as red or black lava rock.

A rare, dense iron-rich metamorphic rock composed of fayalite, iron pyroxene, and almandine garnet.

An iron-rich sedimentary rock, often heavy and rusty-weathering, historically mined as a major source of iron ore.

A coarse-grained, dark mafic intrusive rock that is the plutonic equivalent of basalt, rich in plagioclase and pyroxene.

An opaque, iron-rich basaltic volcanic glass formed by the rapid chilling of basalt lava, darker and denser than rhyolitic obsidian.

An iron-rich peralkaline rhyolite, a silica-rich volcanic rock named for the Italian island of Pantelleria.

A dark, glass-rich volcanic rock of olivine and augite phenocrysts set in a feldspar-free glassy groundmass, named from the Kaiserstuhl region.

A sedimentary rock built from pea-sized concentric spheres called pisoids, often carbonate but sometimes iron or aluminum-rich.

A deep green-and-black stromatolitic jasper, essentially Kambaba Jasper, with circular eye patterns resembling crocodile skin.

A peralkaline rhyolite, a silica-rich volcanic rock with excess alkalis, named for San Pietro Island's Comende district.

A dark green-and-black stromatolite jasper patterned with swirling orbs, formed from fossilized ancient microbial colonies.

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

A calcium- and ferrous-iron-rich tourmaline, the iron analogue of uvite, forming dark brown to black crystals in skarns and metamorphic rocks.