Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Blueschist
A blue-hued, high-pressure metamorphic schist colored by the amphibole glaucophane, formed in cold, deep subduction zones.
metamorphic
Geode
A hollow rock nodule whose interior cavity is lined with inward-pointing crystals such as quartz, amethyst, or calcite.
mineral
Golden Rainbow Obsidian
Black obsidian that displays a golden-to-rainbow iridescent sheen caused by aligned microscopic inclusions reflecting light.
igneous
Larvikite
A Norwegian intrusive rock whose feldspar crystals flash silvery-blue, widely used as blue pearl granite countertops.
igneous
Tillite
A lithified glacial till, a poorly sorted rock of mixed boulders, pebbles and fine matrix that records ancient glaciations.
sedimentary
Biotite Schist
A foliated metamorphic rock dominated by glittering dark biotite mica, formed from mudstones under medium-grade regional metamorphism.
metamorphic
Gold Sheen Obsidian
A black obsidian displaying a golden metallic sheen caused by light reflecting off aligned microscopic gas bubbles or mineral inclusions.
igneous
Oil Shale
A fine-grained sedimentary rock rich in solid organic matter (kerogen) that yields oil and gas when heated.
sedimentary
Septarian Concretion
A rounded sedimentary nodule cracked internally and filled with veins of yellow calcite, prized for its striking dragon-skin patterning.
sedimentary
Naujaite
A sodalite-rich agpaitic nepheline syenite with poikilitic texture from the Ilimaussaq complex, packed with blue sodalite, eudialyte and arfvedsonite.
igneous
Latite
The fine-grained volcanic equivalent of monzonite, an intermediate lava with nearly equal feldspars and little free quartz.
igneous
Tonalite
A quartz-rich plutonic rock dominated by plagioclase feldspar with little alkali feldspar, closely related to granodiorite and quartz diorite.
igneous
Monzonite
An intermediate plutonic rock with nearly equal alkali and plagioclase feldspar and very little quartz, sitting between diorite and syenite.
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
Maxixe
A deep blue beryl with a color caused by radiation that fades in light, named after the Maxixe mine in Brazil.
gemstone
Orange Tourmaline
A warm orange to tangerine tourmaline, an uncommon hue produced by manganese and iron in the crystal.
gemstone
Diabase
A tough, dark, medium-grained igneous rock with the composition of basalt, common in dikes and sills.
igneous
Boninite
A rare high-magnesium andesite formed in young subduction zones, named for Japan's Bonin Islands.
igneous
Peruvian Blue Opal
A translucent common opal from the Andes prized for its serene blue to blue-green color, usually cut into cabochons and beads.
gemstone
Moss Opal
A common opal containing moss- or fern-like mineral inclusions that resemble plants suspended in a pale silica body.
gemstone
Silver
A soft, lustrous white native metal with the highest electrical conductivity, used in jewelry, coinage, and industry.
mineral
Hydroandradite
A hydrous, iron-rich garnet of the hydrogarnet group in which hydroxyl groups substitute for silica within the andradite structure.
mineral
Tinguaite
A fine-grained green phonolitic dike rock rich in nepheline and aegirine, the hypabyssal equivalent of phonolite.
igneous