Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Greensand
A green, glauconite-rich marine sandstone that records slow deposition on continental shelves and is used as a soil amendment.
sedimentary
Anorthosite
An intrusive igneous rock made almost entirely of plagioclase feldspar, famous as the rock of the lunar highlands.
igneousTurritella Jasper
A fossiliferous jasper packed with spiral snail shells, technically a silicified gastropod limestone from Wyoming.
sedimentary
Greenschist
A green, foliated low-grade metamorphic rock colored by chlorite, actinolite, and epidote, marking the greenschist metamorphic facies.
metamorphic
Peridotite
A dense, coarse-grained ultramafic rock rich in olivine that makes up most of the Earth's upper mantle.
igneous
Pegmatite
An exceptionally coarse-grained igneous rock, often granitic, famous for hosting large crystals and many gemstones.
igneous
Norite
A coarse-grained mafic plutonic rock similar to gabbro but with orthopyroxene as the dominant pyroxene instead of clinopyroxene.
igneous
Fire Agate
A rare brown chalcedony containing thin iron-oxide layers that produce flashing, fiery rainbow iridescence like trapped flames.
gemstone
Blueschist
A blue-hued, high-pressure metamorphic schist colored by the amphibole glaucophane, formed in cold, deep subduction zones.
metamorphic
Troctolite
A mafic plutonic rock of plagioclase and olivine whose mottled appearance earned it the nickname 'troutstone'.
igneous
Thunderegg Agate
A nodular rhyolite geode-like ball whose plain exterior hides a star-shaped agate or chalcedony core when cut.
gemstone
Blue Goldstone
A man-made glittering glass colored deep blue with cobalt and studded with tiny copper crystals that mimic a starry night sky.
gemstone
Moss Agate
A translucent chalcedony filled with green or brown dendritic mineral inclusions that resemble moss, foliage, or landscapes.
gemstone
Idaho Star Garnet
Idaho's official state gem: a dark almandine garnet showing a four- or rare six-rayed star from oriented rutile inclusions.
gemstone
Golden Rainbow Obsidian
Black obsidian that displays a golden-to-rainbow iridescent sheen caused by aligned microscopic inclusions reflecting light.
igneousGold Sheen Obsidian
A black obsidian displaying a golden metallic sheen caused by light reflecting off aligned microscopic gas bubbles or mineral inclusions.
igneous
Star Garnet
A rare almandine garnet that displays a four- or six-rayed star (asterism) from oriented rutile inclusions; the state gem of Idaho.
gemstone
Bloodstone
A dark green chalcedony speckled with blood-red spots of iron oxide, traditionally known as heliotrope.
gemstone
Biotite Schist
A foliated metamorphic rock dominated by glittering dark biotite mica, formed from mudstones under medium-grade regional metamorphism.
metamorphic
Sagenite Agate
A chalcedony agate filled with radiating needle-like mineral inclusions, prized for its starburst and spray patterns.
gemstone
Oil Shale
A fine-grained sedimentary rock rich in solid organic matter (kerogen) that yields oil and gas when heated.
sedimentaryNaujaite
A sodalite-rich agpaitic nepheline syenite with poikilitic texture from the Ilimaussaq complex, packed with blue sodalite, eudialyte and arfvedsonite.
igneous
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
Yellow Garnet
A trade term for yellow garnets, including golden grossular, yellow andradite (topazolite), and yellow-green Mali garnet.
gemstone