Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Granodiorite
A common coarse-grained intrusive rock like granite but richer in plagioclase than potassium feldspar.
igneousUnakite Jasper
An altered granite of pink feldspar, green epidote and quartz, mottled pink-and-green and popular as a tumbled and carving stone.
metamorphic
Tonalite
A quartz-rich plutonic rock dominated by plagioclase feldspar with little alkali feldspar, closely related to granodiorite and quartz diorite.
igneous
Geode
A hollow rock nodule whose interior cavity is lined with inward-pointing crystals such as quartz, amethyst, or calcite.
mineral
Latite
The fine-grained volcanic equivalent of monzonite, an intermediate lava with nearly equal feldspars and little free quartz.
igneous
Arkose
A coarse, feldspar-rich sandstone, often pink, that records rapid erosion of granitic source rock under arid conditions.
sedimentarySandstone
A clastic sedimentary rock made of cemented sand grains, often quartz, recording ancient beaches, deserts, and rivers.
sedimentary
Pelitic Schist
A schist derived from clay-rich sediments, rich in mica and often bearing index minerals like garnet, staurolite, or kyanite.
metamorphic
Zebra Jasper
A black-and-white striped chalcedony-quartz rock whose bold zebra-like banding makes it a popular ornamental and lapidary stone.
sedimentary
Graphite Schist
A dark, foliated schist rich in graphite that leaves a grey-black mark and forms from metamorphosed carbon-rich sediments.
metamorphic
Gem Silica
A rare, intensely blue chalcedony colored by copper-rich chrysocolla, prized as the most valuable of the blue chalcedonies.
gemstone
Felsite
A general term for light-colored, fine-grained volcanic rocks rich in quartz and feldspar, like rhyolite.
igneous
Quartzite Sandstone
A tough, quartz-rich sandstone cemented by silica, transitional toward true quartzite but still sedimentary in origin.
sedimentary
Adinole
A fine-grained, sodium-rich contact-metasomatic rock formed where shale is albitized next to intruding diabase or spilite.
metamorphic
Mica Schist
A glittery, strongly foliated rock made mostly of aligned mica flakes that split into thin, shiny sheets.
metamorphic
Dacite
A fine-grained volcanic rock intermediate between andesite and rhyolite, common at explosive stratovolcanoes.
igneous
Metaquartzite
A hard, tough metamorphic rock of fused quartz grains, formed by recrystallizing quartz sandstone under heat and pressure.
metamorphic
Dumortierite
A hard aluminum borosilicate famous for its rich denim-blue color, often forming dense fibrous masses or coloring quartz blue.
mineral
Garnet Schist
A shiny, foliated schist studded with red garnet crystals that grew during medium-grade regional metamorphism.
metamorphic
Granite
A coarse-grained, speckled intrusive rock built from quartz, feldspar, and mica, forming the bedrock of the continents.
igneous
Granulite
A high-grade metamorphic rock formed in the deep, hot crust, marked by anhydrous minerals like pyroxene and garnet.
metamorphic
Shonkinite
A dark, mafic potassic alkaline rock rich in augite with alkali feldspar and often nepheline, classically forming the base of layered sills.
igneous
Paragonite Schist
A pale, silvery schist dominated by paragonite, the sodium-rich white mica, formed in aluminous metamorphic rocks.
metamorphic
Bituminous Shale
A dark, organic-rich shale loaded with kerogen and bitumen that can yield oil and gas, often finely laminated and combustible.
sedimentary