Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Basalt
A fine-grained, dark volcanic rock that erupts as fluid lava and forms most of the ocean floor and many lava plateaus.
igneousFrosted Obsidian
Natural obsidian with a frosted, matte surface produced by weathering, abrasion, or etching rather than a separate variety of glass.
igneous
Black Obsidian
Jet-black natural volcanic glass formed by rapidly cooled lava, prized for its glassy luster and razor-sharp conchoidal fracture.
igneousSmoky Obsidian
Translucent smoky-gray obsidian that transmits a hazy light, intermediate between clear and fully black volcanic glass.
igneous
Devitrified Obsidian
Obsidian that has partly crystallized over time, growing pale spherulite clusters within the black glass, as in snowflake obsidian.
igneousFireworks Obsidian
Black volcanic glass dotted with radiating spherulite bursts that look like exploding fireworks frozen in the stone.
igneous
Snowflake Obsidian
A black volcanic glass speckled with gray-white cristobalite snowflakes, formed as obsidian begins to crystallize.
igneousDouble Flow Obsidian
Obsidian formed from two merged lava flows, producing a stone with two distinct bands of sheen or color.
igneous
Dalmatian Stone
A cream-colored feldspar-and-quartz rock peppered with dark spots, named for its resemblance to a Dalmatian dog.
igneousStone Canyon Jasper
A warm-toned brecciated jasper from central California known for swirling browns, golds, and creams broken by darker seams.
gemstone
Tachylite
An opaque, iron-rich basaltic volcanic glass formed by the rapid chilling of basalt lava, darker and denser than rhyolitic obsidian.
igneous
Gabbro
A coarse-grained, dark mafic intrusive rock that is the plutonic equivalent of basalt, rich in plagioclase and pyroxene.
igneous
Pitchstone
A dull, resinous volcanic glass similar to obsidian but with higher water content and a waxy pitch-like luster.
igneousSard
A brownish-red to deep brown variety of chalcedony, closely related to carnelian but darker, colored by iron oxides.
mineral
Diabase
A tough, dark, medium-grained igneous rock with the composition of basalt, common in dikes and sills.
igneous
Perlite
A hydrated volcanic glass with pearly, onion-like concentric cracks that pops into lightweight white granules when heated.
igneous
Limburgite
A dark, glass-rich volcanic rock of olivine and augite phenocrysts set in a feldspar-free glassy groundmass, named from the Kaiserstuhl region.
igneous
Scoria
A dark, highly vesicular volcanic rock full of gas bubbles, denser than pumice, common as red or black lava rock.
igneous
Black Moonstone
A dark gray-to-black feldspar variety of moonstone that shows blue and white adularescent flash against a smoky body.
gemstone
Honduran Opal
Precious opal from Honduras occurring in a dark volcanic matrix, where bright flecks of color flash against a natural black basalt background.
gemstone
Angelite
A soft pale-blue calcium sulfate, the anhydrous form of gypsum, prized as a gentle, calming tumbled stone.
mineralDallasite Jasper
A green-and-white volcanic breccia from Vancouver Island, cemented by jasper and rich in epidote, popular as a regional lapidary stone.
gemstoneUnakite Jasper
An altered granite of pink feldspar, green epidote and quartz, mottled pink-and-green and popular as a tumbled and carving stone.
metamorphic
Bloodstone
A dark green chalcedony speckled with blood-red spots of iron oxide, traditionally known as heliotrope.
gemstone