Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Pele's Tears
Small, smooth, teardrop-shaped beads of basaltic volcanic glass formed from airborne lava droplets, often paired with Pele's hair.
igneous
Prasiolite
A pale green variety of quartz, usually created by heat-treating amethyst, often marketed as green amethyst.
gemstone
Tachylite
An opaque, iron-rich basaltic volcanic glass formed by the rapid chilling of basalt lava, darker and denser than rhyolitic obsidian.
igneousViolet Obsidian
A violet-to-purple glass sold as obsidian; uniform purple material is almost always manufactured glass rather than natural volcanic obsidian.
igneous
Sideromelane
A transparent, pale brown basaltic volcanic glass formed when basalt lava is quenched extremely fast, often underwater.
igneous
Pele's Hair
Fine, golden, hair-like strands of basaltic volcanic glass spun from fluid lava droplets during eruptions, named for the Hawaiian volcano goddess.
igneous
Purple Opal
A purple-hued common opal, much of it the Mexican "morado" type, valued for even violet color rather than play-of-color.
gemstonePurple Sheen Obsidian
Black volcanic glass that reveals a soft purple-to-violet sheen at certain angles, caused by light interference off aligned inclusions.
igneous
Andamooka Opal
Precious opal from the Andamooka field of South Australia, famous for solid crystal opal and its distinctive treatable matrix opal.
gemstone
Purple Tourmaline
An uncommon purple to violet tourmaline colored by manganese, the deeper reddish-purple stones sometimes called siberite.
gemstone
Kunzite
The delicate pink-to-lilac variety of spodumene, a lithium silicate prized for soft color and strong pleochroism but tricky perfect cleavage.
gemstone
Spirit Quartz
A South African quartz whose central crystal is coated in tiny druzy points, also called cactus or fairy quartz.
crystal
Grape Agate
Clusters of tiny botryoidal chalcedony spheres resembling bunches of grapes, famously purple, found in Indonesia.
mineralSuper Seven
A trade name for quartz containing a combination of seven minerals including amethyst, smoky quartz, and cacoxenite, prized by collectors.
crystal
Cathedral Quartz
Quartz with a stepped, multi-pointed structure of parallel side crystals resembling the spires of a cathedral.
crystal
Diabase
A tough, dark, medium-grained igneous rock with the composition of basalt, common in dikes and sills.
igneous
Tiger Iron
A banded combination rock of golden tiger's eye, red jasper, and metallic hematite, formed in ancient iron deposits.
metamorphic
Metabasalt
Basalt that has been metamorphosed, developing new minerals like chlorite, actinolite, and epidote that give it a greenish color.
metamorphic
Limburgite
A dark, glass-rich volcanic rock of olivine and augite phenocrysts set in a feldspar-free glassy groundmass, named from the Kaiserstuhl region.
igneousTintenbar Opal
Rare precious opal from Tintenbar in northern New South Wales, Australia, occurring in volcanic basalt rather than sedimentary rock.
gemstone
Geode
A hollow rock nodule whose interior cavity is lined with inward-pointing crystals such as quartz, amethyst, or calcite.
mineral
Emerald Crystal
The natural crystalline form of emerald, the prized green chromium-and-vanadium variety of beryl and the May birthstone.
crystal
Ametrine
A natural bicolor quartz that combines purple amethyst and golden citrine in a single crystal.
crystal
Citrine
The golden-yellow variety of quartz, ranging from pale lemon to deep madeira amber, often produced by heating amethyst.
gemstone