Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Chert
A hard, fine-grained sedimentary silica rock that breaks with sharp conchoidal edges, prized by ancient toolmakers.
sedimentary
Calcarenite
Sand-grained limestone composed of carbonate particles such as shell fragments and ooids cemented into a calcite rock.
sedimentary
Ijolite
A coarse-grained, feldspar-free plutonic rock composed mainly of nepheline and sodic pyroxene, the intrusive equivalent of nephelinite.
igneousOwyhee Blue Jasper
A soft blue-gray jasper from the Owyhee region of Oregon and Idaho, prized for its rare, calming blue tones among earthy jaspers.
gemstone
Potassium Feldspar
The potassium-rich feldspar group - orthoclase, microcline, and sanidine - a major rock-forming mineral often recognized by its salmon-pink color.
mineral
Metabasalt
Basalt that has been metamorphosed, developing new minerals like chlorite, actinolite, and epidote that give it a greenish color.
metamorphic
Anorthosite
An intrusive igneous rock made almost entirely of plagioclase feldspar, famous as the rock of the lunar highlands.
igneous
Siltstone
A fine-grained clastic rock of silt-sized grains, intermediate between sandstone and mudstone, with a gritty feel.
sedimentary
Limburgite
A dark, glass-rich volcanic rock of olivine and augite phenocrysts set in a feldspar-free glassy groundmass, named from the Kaiserstuhl region.
igneous
Staurolite Schist
A mica schist studded with brown staurolite porphyroblasts, sometimes forming the cross-shaped twins known as fairy stones.
metamorphic
Vogesite
A dark hornblende-rich lamprophyre dike rock with amphibole and augite phenocrysts in an alkali-feldspar-dominated groundmass.
igneous
Patronite
A rare greenish-black vanadium sulfide that was historically one of the world's most important ores of vanadium.
mineral
Fossiliferous Limestone
Calcium-carbonate sedimentary rock packed with visible fossils, recording ancient marine life within an easily scratched, fizzing matrix.
sedimentaryTripolite
A soft, lightweight siliceous sedimentary rock made of fossil diatom remains, prized as a fine natural abrasive and polishing powder.
sedimentary
Mylonite
A fine-grained, strongly foliated rock formed deep in fault zones where rocks flowed and ground down rather than fracturing.
metamorphic
Banded Iron Formation
Ancient chemically deposited rock of alternating iron-oxide and silica bands recording Earth's early oxygenation and a major iron ore source.
sedimentary
Glaucophane Schist
A blue, high-pressure metamorphic schist rich in glaucophane, the classic rock of subduction zones, also known as blueschist.
metamorphic
Mudstone
A fine-grained sedimentary rock of compacted clay and silt that, unlike shale, breaks in blocks rather than thin layers.
sedimentary
Felsite
A general term for light-colored, fine-grained volcanic rocks rich in quartz and feldspar, like rhyolite.
igneous
Dolomite
A calcium-magnesium carbonate mineral and rock similar to limestone but harder and only weakly reactive to acid.
mineral
Black Shale
Dark, organic-rich fine-grained sedimentary rock formed in oxygen-poor waters, often a source rock for oil and gas.
sedimentary
Tillite
A lithified glacial till, a poorly sorted rock of mixed boulders, pebbles and fine matrix that records ancient glaciations.
sedimentary
Turbidite
A graded sedimentary deposit laid down by underwater turbidity currents, recording avalanches of sediment cascading down submarine slopes.
sedimentary
Phonolite
A silica-poor volcanic rock of alkali feldspar and feldspathoids that rings when struck, hence 'clinkstone.'
igneous