Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Argillite
Hardened, fine-grained mudrock intermediate between shale and slate, dense and non-fissile, often carved into ornaments.
sedimentaryTripolite
A soft, lightweight siliceous sedimentary rock made of fossil diatom remains, prized as a fine natural abrasive and polishing powder.
sedimentarySlate
A fine-grained, low-grade metamorphic rock that splits into flat sheets along slaty cleavage, long used for roofing and flooring.
metamorphicSandstone
A clastic sedimentary rock made of cemented sand grains, often quartz, recording ancient beaches, deserts, and rivers.
sedimentary
Diabase
A tough, dark, medium-grained igneous rock with the composition of basalt, common in dikes and sills.
igneous
Lamprophyre
A dark, mineral-rich dike rock with abundant mica or amphibole phenocrysts set in a fine groundmass, often associated with gold and diamonds.
igneous
Rhyolite
A fine-grained, silica-rich volcanic rock that is the extrusive equivalent of granite, often pale, banded, or flow-textured.
igneous
Gabbro
A coarse-grained, dark mafic intrusive rock that is the plutonic equivalent of basalt, rich in plagioclase and pyroxene.
igneous
Adinole
A fine-grained, sodium-rich contact-metasomatic rock formed where shale is albitized next to intruding diabase or spilite.
metamorphic
Cordierite Hornfels
A tough, fine-grained contact-metamorphic rock containing cordierite, often spotted, formed by heat from nearby igneous intrusions.
metamorphic
Chalk
A soft, white, fine-grained limestone made almost entirely of microscopic marine plankton skeletons.
sedimentary
Dalmatian Jasper
A cream-colored spotted stone resembling a Dalmatian dog, made of feldspar and quartz dotted with dark mineral grains.
igneous
Trachyte
A fine-grained volcanic rock dominated by alkali feldspar, the extrusive equivalent of syenite.
igneous
Dacite
A fine-grained volcanic rock intermediate between andesite and rhyolite, common at explosive stratovolcanoes.
igneous
Wacke
A poorly sorted, muddy sandstone with abundant clay matrix between its grains, typically dark and deposited by turbidity currents.
sedimentary
Novaculite
An extremely fine-grained, dense siliceous rock famous as Arkansas whetstone, prized for sharpening fine cutting tools.
sedimentary
Latite
The fine-grained volcanic equivalent of monzonite, an intermediate lava with nearly equal feldspars and little free quartz.
igneousChalky Limestone
A soft, fine-grained, porous white limestone made largely of microscopic calcareous plankton skeletons, the rock that forms classic white cliffs.
sedimentary
Sapropel
A soft, dark, organic-rich mud deposited in stagnant, oxygen-poor water, a key precursor to oil and gas source rocks.
sedimentaryPipestone
A soft, fine-grained red metamorphosed claystone, sacred to many Native American peoples and carved into ceremonial pipes.
metamorphicSpiderweb Jasper
A jasper crossed by fine dark veins forming a spiderweb-like network, often a brecciated stone cemented by darker matrix.
mineralLithographic Limestone
Extremely fine-grained, even-textured limestone famous for lithographic printing and for preserving exquisite fossils like Archaeopteryx.
sedimentary
Granodiorite
A common coarse-grained intrusive rock like granite but richer in plagioclase than potassium feldspar.
igneous
Hornblende Schist
A dark, foliated schist rich in needle-like hornblende crystals, formed by metamorphism of mafic igneous rocks.
metamorphic