Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Emerald in Matrix
Natural emerald crystals still embedded in their host rock, prized as mineral specimens that show how the gem grew in place.
gemstone
Aquamarine Matrix
Aquamarine crystals still attached to their natural host rock, prized as mineral specimens showing beryl in its original pocket setting.
mineralMarl
A soft, earthy sedimentary rock made of a mixture of calcium carbonate and clay, intermediate between limestone and mudstone.
sedimentary
Shelly Limestone
A limestone packed with visible shells and shell fragments, recording the accumulation of marine invertebrate remains on ancient sea floors.
sedimentary
Aragonite
A calcium carbonate mineral and polymorph of calcite, aragonite forms distinctive needle clusters, sea shells, and pearls.
mineral
Calc-schist
A foliated metamorphic rock of calcite mixed with mica, quartz, and calc-silicate minerals, derived from marly sediments.
metamorphic
Crocoite
A striking lead chromate mineral prized for its brilliant orange-red prismatic crystals, with the finest specimens from Tasmania.
mineral
Coquina
A soft, porous limestone made of loosely cemented shell and coral fragments, used as a coastal building stone.
sedimentary
Aquamarine Crystal
The blue iron-bearing variety of beryl, forming clear hexagonal crystals prized both as specimens and as a March birthstone gem.
crystal
Mushroom Tourmaline
A rare mushroom-shaped tourmaline growth habit, typically magnesium-rich dravite/uvite, prized by collectors for its fungus-like cap-and-stem form.
mineral
Emerald Crystal
The natural crystalline form of emerald, the prized green chromium-and-vanadium variety of beryl and the May birthstone.
crystalDiatomaceous Earth
Soft, lightweight siliceous rock made of fossilized diatom shells, valued as a filter, abrasive, and absorbent.
sedimentary
Migmatite
A 'mixed rock' showing swirling light and dark bands, formed where high-grade metamorphism causes rock to begin partially melting.
metamorphic
Calcarenite
Sand-grained limestone composed of carbonate particles such as shell fragments and ooids cemented into a calcite rock.
sedimentary
Sperrylite
A rare platinum arsenide and the most important platinum-bearing mineral, forming bright metallic cubic crystals.
mineral
Glauconite
A soft, green iron-potassium mica that forms in marine sediments and gives greensand its characteristic olive color.
mineral
Coal
A combustible black sedimentary rock formed from ancient plant matter and burned for centuries as a primary fossil fuel.
sedimentary
Celsian
A rare barium-rich feldspar that forms in manganese and barium-enriched metamorphic and hydrothermal deposits, the barium end-member of the feldspar family.
mineral
Talc
The softest mineral on the Mohs scale, talc has a greasy, soapy feel and is the source of talcum powder and soapstone.
mineral
Euxenite
A black rare-earth niobium-tantalum oxide, often radioactive and metamict, mined for yttrium, niobium, and associated rare elements.
mineral
Baddeleyite
A natural zirconium dioxide mineral, hard and refractory, valued as a zirconium source and prized for high-precision U-Pb dating.
mineral
Halite
The natural mineral form of table salt, a soft, water-soluble evaporite that forms perfect cubic crystals and tastes salty.
mineral
Shungite
A rare black carbon-rich rock from Russia, noted for containing fullerenes and ranging from dull mineralized stone to lustrous noble shungite.
sedimentarySuper Seven
A trade name for quartz containing a combination of seven minerals including amethyst, smoky quartz, and cacoxenite, prized by collectors.
crystal