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
Granodiorite
A common coarse-grained intrusive rock like granite but richer in plagioclase than potassium feldspar.
igneous
Arkose
A coarse, feldspar-rich sandstone, often pink, that records rapid erosion of granitic source rock under arid conditions.
sedimentary
Gabbro
A coarse-grained, dark mafic intrusive rock that is the plutonic equivalent of basalt, rich in plagioclase and pyroxene.
igneous
Migmatite
A 'mixed rock' showing swirling light and dark bands, formed where high-grade metamorphism causes rock to begin partially melting.
metamorphic
Garnierite
A vivid green hydrous nickel-magnesium silicate that is a major ore of nickel, mined from weathered ultramafic rocks.
mineral
Ferricrete
Hard surface crust formed when iron oxides cement soil and sediment into a rusty, durable duricrust in tropical and weathered terrains.
sedimentaryQuartz Arenite
A clean, mature sandstone made almost entirely of quartz grains, representing extreme weathering, sorting, and recycling of sediment.
sedimentary
Ironstone
An iron-rich sedimentary rock, often heavy and rusty-weathering, historically mined as a major source of iron ore.
sedimentary
Tillite
A lithified glacial till, a poorly sorted rock of mixed boulders, pebbles and fine matrix that records ancient glaciations.
sedimentary
Lake Michigan Agate
Glacially deposited banded agates found along Lake Michigan beaches, small waterworn pebbles with concentric red and grey banding.
gemstoneLake Huron Agate
Glacially transported banded agates found along Lake Huron's shores, typically small, frosted pebbles with red-orange iron banding.
gemstone
Wolframite
Wolframite is the historic principal ore of tungsten, a heavy black tungstate forming bladed crystals in granite veins.
mineral
Rhyolite
A fine-grained, silica-rich volcanic rock that is the extrusive equivalent of granite, often pale, banded, or flow-textured.
igneous
Feldspar
The most abundant mineral group in Earth's crust, feldspars are aluminosilicates that form much of granite and many igneous rocks.
mineral
Chrome Pyrope
A chromium-rich pyrope garnet whose intense blood-red color comes from chromium, often mined from ant hills and kimberlite weathering.
gemstone
Cleavelandite
A striking platy, blade-like variety of albite feldspar that grows in fanned aggregates of thin white crystals within granite pegmatites.
mineral
Orthoclase
A common rock-forming potassium feldspar, the Mohs hardness reference at 6, found in granites and used in ceramics and glassmaking.
mineral
Feldspathic Sandstone
A feldspar-rich sandstone, often pink, that points to granitic source rocks eroded quickly in dry or cold climates.
sedimentary
Rubicline
An extremely rare rubidium-dominant alkali feldspar, the rubidium analogue of microcline, found in rare-element granitic pegmatites.
mineral
Pele's Hair
Fine, golden, hair-like strands of basaltic volcanic glass spun from fluid lava droplets during eruptions, named for the Hawaiian volcano goddess.
igneous
Imperial Garnet
A trade name for high-brilliance golden grossular-andradite (grandite) garnet, most associated with the Mali deposits of West Africa.
gemstone
Mali Garnet
A rare grossular-andradite blend ('grandite') from Mali, prized for its high brilliance and golden-green to yellow color.
gemstone
Pele's Tears
Small, smooth, teardrop-shaped beads of basaltic volcanic glass formed from airborne lava droplets, often paired with Pele's hair.
igneous