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.

A high-grade metamorphic gneiss of garnet, sillimanite, quartz, and graphite, derived from ancient aluminous sediments.

A high-grade metamorphic rock formed in the deep, hot crust, marked by anhydrous minerals like pyroxene and garnet.

A foliated schist threaded with black tourmaline (schorl) needles, marking boron-rich metamorphic or metasomatic conditions.

A metamorphic rock of calcium-rich silicate minerals formed from impure limestone or dolomite altered by heat and fluids.

A mica schist studded with brown staurolite porphyroblasts, sometimes forming the cross-shaped twins known as fairy stones.

A metasomatic rock formed when alkali-rich fluids from carbonatite or alkaline intrusions transform surrounding country rock.

A 'mixed rock' showing swirling light and dark bands, formed where high-grade metamorphism causes rock to begin partially melting.

A coarse-grained, speckled intrusive rock built from quartz, feldspar, and mica, forming the bedrock of the continents.

A fine-grained, strongly foliated rock formed deep in fault zones where rocks flowed and ground down rather than fracturing.

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

A general term for light-colored, fine-grained volcanic rocks rich in quartz and feldspar, like rhyolite.

The blue-grey relative of tiger's eye, a chatoyant quartz showing a shifting band of light like a bird of prey's eye.

Clear quartz filled with mineral inclusions that look like underwater gardens, mossy landscapes, or floating scenery.

A black-and-white striped chalcedony-quartz rock whose bold zebra-like banding makes it a popular ornamental and lapidary stone.