Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Dunite
An ultramafic intrusive rock made almost entirely of olivine, representing mantle material.
igneous
Limestone
A soft carbonate sedimentary rock made mostly of calcite, often packed with marine fossils and prone to forming caves.
sedimentaryUrtite
A pale, nepheline-dominated plutonic rock at the leucocratic end of the ijolite series, sometimes associated with major apatite ore deposits.
igneous
Reedmergnerite
A rare boron-bearing feldspar, the boron analogue of albite, first found in oil-shale nodules of the Green River Formation.
mineral
Albitite
A pale rock made almost entirely of the sodium feldspar albite, formed by sodic magmatism or sodium metasomatism.
igneousMint Opal
A soft mint-green variety of common opal, usually opaque and colored by trace copper or nontronite inclusions rather than play-of-color.
gemstoneEulysite
A rare, dense iron-rich metamorphic rock composed of fayalite, iron pyroxene, and almandine garnet.
metamorphic
Breccia
A coarse rock of angular, sharp-edged fragments cemented in a matrix, marking nearby rockfall, faulting, or impact.
sedimentary
Scoria
A dark, highly vesicular volcanic rock full of gas bubbles, denser than pumice, common as red or black lava rock.
igneous
Menilite Opal
An opaque grey-brown common opal forming nodules and concretions, historically called liver opal for its dull brownish color.
mineral
Tsavorite Garnet
A brilliant green grossular garnet colored by chromium and vanadium, rivaling emerald with superior brilliance and durability.
gemstone
Coquina
A soft, porous limestone made of loosely cemented shell and coral fragments, used as a coastal building stone.
sedimentaryPrase
An old name for a dull leek-green variety of quartz or chalcedony colored by green mineral inclusions, historically called mother of emerald.
crystal
Basalt
A fine-grained, dark volcanic rock that erupts as fluid lava and forms most of the ocean floor and many lava plateaus.
igneousAmegreen
A natural bicolor quartz blending amethyst purple with prasiolite green in a single crystal, prized as a metaphysical heart-crown stone.
crystal
Diorite
A coarse-grained intrusive rock with a distinctive salt-and-pepper look, the plutonic equivalent of andesite.
igneous
Malachite
A vivid green copper carbonate mineral famous for swirling concentric bands, used as an ore of copper and an ornamental gemstone.
mineral
Greensand
A green, glauconite-rich marine sandstone that records slow deposition on continental shelves and is used as a soil amendment.
sedimentary
Hornfels
A tough, fine-grained, non-foliated rock formed by the intense heat of nearby magma baking surrounding rock at contact zones.
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
Ijolite
A coarse-grained, feldspar-free plutonic rock composed mainly of nepheline and sodic pyroxene, the intrusive equivalent of nephelinite.
igneous
Radiolarite
A hard, fine-grained siliceous rock built from the microscopic silica skeletons of radiolarians, often forming colorful ribbon-banded cherts.
sedimentary
Pisolite
A sedimentary rock built from pea-sized concentric spheres called pisoids, often carbonate but sometimes iron or aluminum-rich.
sedimentary
Skarn
A calc-silicate rock formed by chemical exchange between magma and carbonate rock, often rich in garnet and economically important ore minerals.
metamorphic