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

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

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

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

A fine-grained, silica-rich volcanic rock that is the extrusive equivalent of granite, often pale, banded, or flow-textured.

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

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

A granite-like rock containing orthopyroxene, formed at high temperatures and pressures and often classed with the granulites.

A nodular rhyolite geode-like ball whose plain exterior hides a star-shaped agate or chalcedony core when cut.

A rare granitic rock containing concentric, onion-like spheres called orbicules, prized as a striking ornamental stone.

A striking platy, blade-like variety of albite feldspar that grows in fanned aggregates of thin white crystals within granite pegmatites.

A hydrated volcanic glass with pearly, onion-like concentric cracks that pops into lightweight white granules when heated.