Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Aragonite
A calcium carbonate mineral and polymorph of calcite, aragonite forms distinctive needle clusters, sea shells, and pearls.
mineral
Caliche
A hardened soil crust cemented by calcium carbonate, forming a tough whitish layer common in arid and semi-arid regions.
sedimentary
Onyx Marble
Translucent banded calcium-carbonate stone deposited in caves and springs, prized for ornamental carvings despite its softness.
sedimentary
Travertine
A banded, porous limestone deposited by mineral springs, prized as a warm-toned natural building and tile stone.
sedimentary
Septarian Concretion
A rounded sedimentary nodule cracked internally and filled with veins of yellow calcite, prized for its striking dragon-skin patterning.
sedimentary
Calcite
An extremely common calcium carbonate mineral that comes in nearly every color and shows strong double refraction in clear crystals.
mineral
Calcrete
Carbonate-cemented soil crust formed in arid regions where calcium carbonate accumulates and hardens within the regolith.
sedimentary
Orange Calcite
A soft, glowing orange variety of calcite colored by iron oxides, popular as tumbled stones and known for fizzing in acid.
mineral
Feruvite
A calcium- and ferrous-iron-rich tourmaline, the iron analogue of uvite, forming dark brown to black crystals in skarns and metamorphic rocks.
mineral
Anorthite
The calcium end-member of the plagioclase feldspar series, a high-temperature mineral common in mafic rocks, meteorites and lunar samples.
mineral
Calcirudite
A coarse-grained limestone built of gravel-sized carbonate clasts, the carbonate equivalent of a conglomerate or breccia.
sedimentary
Bytownite
A calcium-rich plagioclase feldspar between labradorite and anorthite, faceted as transparent golden-yellow gems sometimes sold as yellow labradorite.
gemstone
Plagioclase
The most abundant rock-forming feldspar group, a continuous solid-solution series from sodium albite to calcium anorthite that builds much of the crust.
mineral
Pearl
An organic gem formed inside mollusks from layered nacre, prized for its iridescent luster and classic elegance.
gemstone
Calc-schist
A foliated metamorphic rock of calcite mixed with mica, quartz, and calc-silicate minerals, derived from marly sediments.
metamorphic