Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Seam Agate
Agate that forms in flat cracks or veins of host rock rather than rounded nodules, producing straight, parallel banding.
gemstone
Calc-schist
A foliated metamorphic rock of calcite mixed with mica, quartz, and calc-silicate minerals, derived from marly sediments.
metamorphic
Graphite Schist
A dark, foliated schist rich in graphite that leaves a grey-black mark and forms from metamorphosed carbon-rich sediments.
metamorphicImperial Jasper
A prized Mexican jasper known for pastel green, lavender, and cream orbicular patterns that take an exceptional polish.
mineral
Blue Jasper
An opaque blue variety of chalcedony jasper, less common than red or green forms, colored by mineral inclusions.
mineralMorrisonite Jasper
A rare, prized Oregon picture jasper known for blue-green orbs and scenic patterns, often called the king of jaspers.
mineralExotica Jasper
Also called Sci-Fi Jasper, a Mexican jasper-rhyolite with swirling abstract patterns in cream, tan, gray, pink, and green.
gemstone
Mustard Jasper
A warm mustard-to-ochre yellow jasper colored by iron, valued by lapidaries for its rich, earthy golden tone.
gemstone
Obsidian
A glassy, jet-black volcanic rock formed when lava cools too fast to crystallize, prized for razor-sharp conchoidal edges.
igneous
Shungite
A rare black carbon-rich rock from Russia, noted for containing fullerenes and ranging from dull mineralized stone to lustrous noble shungite.
sedimentary
Anthracite
The highest-rank coal, a hard, lustrous black rock that burns cleanly with little smoke and high heat output.
metamorphic
Thulite
A pink, manganese-rich variety of zoisite used as an ornamental gemstone, often mottled with white quartz and grey matrix.
gemstone
Vogesite
A dark hornblende-rich lamprophyre dike rock with amphibole and augite phenocrysts in an alkali-feldspar-dominated groundmass.
igneous
Gahnite
A hard zinc-rich member of the spinel group, usually dark blue-green to black, forming octahedral crystals in metamorphic and pegmatitic rocks.
mineral
Chrysocolla
A vivid blue-green hydrated copper silicate, soft on its own but prized as a gem when hardened by intergrown quartz or chalcedony.
mineral
Lignite
The lowest rank of coal, a soft brown carbon-rich rock formed from compacted peat, used mainly for electricity generation.
sedimentary
Potassium Feldspar
The potassium-rich feldspar group - orthoclase, microcline, and sanidine - a major rock-forming mineral often recognized by its salmon-pink color.
mineral
Argillite
Hardened, fine-grained mudrock intermediate between shale and slate, dense and non-fissile, often carved into ornaments.
sedimentary
Needle Tourmaline
Fine acicular (needle-like) tourmaline crystals, often black schorl, frequently seen as slender inclusions within clear quartz.
mineral
Crinoidal Limestone
A fossiliferous limestone built largely from the disc-shaped skeletal plates of crinoids, marine animals known as sea lilies.
sedimentary
Jaspillite
A banded, metamorphosed iron formation in which bright red jasper alternates with silvery hematite or magnetite layers.
metamorphic
Schorlomite
A lustrous black titanium-rich garnet of the andradite series, found in alkaline igneous rocks like nepheline syenite and ijolite.
mineral
Feldspathic Sandstone
A feldspar-rich sandstone, often pink, that points to granitic source rocks eroded quickly in dry or cold climates.
sedimentary
Diabase
A tough, dark, medium-grained igneous rock with the composition of basalt, common in dikes and sills.
igneous