Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Gneiss
A high-grade metamorphic rock defined by alternating light and dark mineral bands, formed under intense heat and pressure.
metamorphic
Banded Iron Formation
Ancient chemically deposited rock of alternating iron-oxide and silica bands recording Earth's early oxygenation and a major iron ore source.
sedimentary
Calc-Silicate Rock
A metamorphic rock of calcium-rich silicate minerals formed from impure limestone or dolomite altered by heat and fluids.
metamorphicAsphalt Rock
A porous sedimentary rock naturally saturated with bitumen, dark, tarry-smelling, and historically mined for paving.
sedimentary
Khondalite
A high-grade metamorphic gneiss of garnet, sillimanite, quartz, and graphite, derived from ancient aluminous sediments.
metamorphic
Migmatite
A 'mixed rock' showing swirling light and dark bands, formed where high-grade metamorphism causes rock to begin partially melting.
metamorphic
Mylonite
A fine-grained, strongly foliated rock formed deep in fault zones where rocks flowed and ground down rather than fracturing.
metamorphic
Fenite
A metasomatic rock formed when alkali-rich fluids from carbonatite or alkaline intrusions transform surrounding country rock.
metamorphic
Granulite
A high-grade metamorphic rock formed in the deep, hot crust, marked by anhydrous minerals like pyroxene and garnet.
metamorphic
Melteigite
A dark, pyroxene-dominated plutonic rock at the mafic end of the ijolite series, made mainly of aegirine-augite with subordinate nepheline.
igneous
Staurolite Schist
A mica schist studded with brown staurolite porphyroblasts, sometimes forming the cross-shaped twins known as fairy stones.
metamorphic
Jaspillite
A banded, metamorphosed iron formation in which bright red jasper alternates with silvery hematite or magnetite layers.
metamorphic
Metaconglomerate
A conglomerate altered by heat and pressure, often with its rounded pebbles stretched and flattened into elongated lenses.
metamorphic
Kakortokite
A spectacularly banded agpaitic nepheline syenite of alternating red eudialyte, black amphibole and white feldspar layers from Ilimaussaq, Greenland.
igneous
Kentucky Agate
The official state rock of Kentucky, a banded agate famous for striking deep-red and black fortification patterns.
gemstoneWonderstone
A banded rhyolitic volcanic rock with swirling tan, red, and yellow iron-oxide layers prized as a decorative picture stone.
igneous
Scoria
A dark, highly vesicular volcanic rock full of gas bubbles, denser than pumice, common as red or black lava rock.
igneous
Seam Agate
Agate that forms in flat cracks or veins of host rock rather than rounded nodules, producing straight, parallel banding.
gemstone
Basalt
A fine-grained, dark volcanic rock that erupts as fluid lava and forms most of the ocean floor and many lava plateaus.
igneous
Radiolarite
A hard, fine-grained siliceous rock built from the microscopic silica skeletons of radiolarians, often forming colorful ribbon-banded cherts.
sedimentary
Jacupirangite
A rare dark ultramafic alkaline igneous rock built mostly of titanaugite and magnetite, named for Jacupiranga in Brazil.
igneous
Biotite Schist
A foliated metamorphic rock dominated by glittering dark biotite mica, formed from mudstones under medium-grade regional metamorphism.
metamorphicZebra Agate
A banded chalcedony agate with bold alternating dark and light stripes resembling zebra markings, sometimes color-enhanced.
gemstone
Pseudotachylite
A dark, glassy rock formed when frictional heat from fault movement or impact melts rock along narrow veins.
metamorphic