Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Arkose
A coarse, feldspar-rich sandstone, often pink, that records rapid erosion of granitic source rock under arid conditions.
sedimentary
Sperrylite
A rare platinum arsenide and the most important platinum-bearing mineral, forming bright metallic cubic crystals.
mineral
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.
mineralHutcheonite
A titanium-aluminum garnet discovered in calcium-aluminum inclusions of the Allende meteorite, recording the earliest history of the solar system.
mineral
Olenite
A rare aluminum-rich species of the tourmaline group, usually colorless to pale, named for the Olenii Range in Russia's Kola Peninsula.
mineral
Buergerite
A rare iron-rich (ferric) species of the tourmaline group, dark brown to bronze-black, named after crystallographer Martin Buerger.
mineralAppinite
A group of coarse, water-rich plutonic rocks dominated by large hornblende crystals set in feldspar, intermediate between lamprophyre and diorite.
igneous
Kentucky Agate
The official state rock of Kentucky, a banded agate famous for striking deep-red and black fortification patterns.
gemstone
Verdite
A rich green, fuchsite-rich metamorphic rock from southern Africa, prized as a carving and ornamental stone.
metamorphic
Shadow Agate
A banded agate that displays a moving shadow or flash across its surface when tilted under light, caused by closely spaced parallel bands.
gemstone
Talc
The softest mineral on the Mohs scale, talc has a greasy, soapy feel and is the source of talcum powder and soapstone.
mineralSuper Seven
A trade name for quartz containing a combination of seven minerals including amethyst, smoky quartz, and cacoxenite, prized by collectors.
crystal
Alnöite
A rare dark ultramafic lamprophyre rich in melilite, biotite and olivine, named for Alnö Island in Sweden.
igneous
Pegmatite
An exceptionally coarse-grained igneous rock, often granitic, famous for hosting large crystals and many gemstones.
igneous
Euxenite
A black rare-earth niobium-tantalum oxide, often radioactive and metamict, mined for yttrium, niobium, and associated rare elements.
mineral
Anorthite
The calcium end-member of the plagioclase feldspar series, a high-temperature mineral common in mafic rocks, meteorites and lunar samples.
mineral
Lapis Lazuli
An intensely blue metamorphic rock of lazurite flecked with golden pyrite, prized for millennia as a gemstone and ultramarine pigment.
metamorphic
Andesite
A fine-grained, intermediate volcanic rock common at subduction-zone volcanoes, between basalt and rhyolite in composition.
igneous
Bruneau Jasper
A prized Idaho picture jasper from Bruneau Canyon known for brown and cream orbicular egg-rock patterns and scenic landscapes.
mineral
Clear Quartz
The pure, colorless form of crystalline quartz, valued for its clarity, abundance, and piezoelectric properties used in electronics.
crystal
Amphibolite
A dark, dense metamorphic rock dominated by hornblende and plagioclase, formed by medium- to high-grade metamorphism of basalt.
metamorphic
Epidosite
A hard, pistachio-green rock composed mainly of epidote and quartz, formed by hydrothermal alteration of mafic rocks.
metamorphic
Glauconite
A soft, green iron-potassium mica that forms in marine sediments and gives greensand its characteristic olive color.
mineral
Coquina
A soft, porous limestone made of loosely cemented shell and coral fragments, used as a coastal building stone.
sedimentary