Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Bituminous Shale
A dark, organic-rich shale loaded with kerogen and bitumen that can yield oil and gas, often finely laminated and combustible.
sedimentary
Mandarin Garnet
The intensely glowing orange variety of spessartine garnet, prized for its pure 'Fanta-orange' fire and high brilliance.
gemstone
Cinnamon Stone
The warm cinnamon-to-honey-brown variety of grossular garnet, also known as hessonite, with a characteristic swirly internal texture.
gemstone
Black Shale
Dark, organic-rich fine-grained sedimentary rock formed in oxygen-poor waters, often a source rock for oil and gas.
sedimentary
Coral Rock
A porous limestone built from the calcium carbonate skeletons of corals and reef organisms, the lithified remains of ancient or modern reefs.
sedimentary
Cacholong Opal
An opaque, porcelain-white common opal prized for its milky, pearl-like appearance and high porosity, often carved or beaded.
gemstone
Lamprophyre
A dark, mineral-rich dike rock with abundant mica or amphibole phenocrysts set in a fine groundmass, often associated with gold and diamonds.
igneousGreen Jade
The classic green ornamental gem, either jadeite or nephrite, valued for millennia for its toughness and rich color, especially imperial green.
gemstone
Jade
A tough, prized ornamental gem that is actually two distinct minerals, jadeite and nephrite, revered for millennia in many cultures.
gemstone
Oil Shale
A fine-grained sedimentary rock rich in solid organic matter (kerogen) that yields oil and gas when heated.
sedimentary
Carnelian
A warm orange-to-red variety of chalcedony quartz colored by iron oxide, used since antiquity for seals, beads, and cabochons.
gemstone
Spirit Quartz
A South African quartz whose central crystal is coated in tiny druzy points, also called cactus or fairy quartz.
crystal
Hydrogrossular Garnet
A water-bearing massive grossular garnet, usually green or pink, widely used as a tough jade-like carving stone.
gemstone
Carnotite
A bright yellow, radioactive potassium uranyl vanadate that is a major ore of both uranium and vanadium.
mineral
Sapropel
A soft, dark, organic-rich mud deposited in stagnant, oxygen-poor water, a key precursor to oil and gas source rocks.
sedimentary
Proustite
A scarlet-red silver arsenic sulfide known as light ruby silver, a striking but light-sensitive ore that darkens on exposure.
mineral
Franklinite
A black spinel-group zinc iron oxide, essentially unique to Franklin, New Jersey, where it was a key zinc and manganese ore.
mineral
Calaverite
A brass- to silver-yellow gold telluride that is a major gold ore, famous from Cripple Creek and Kalgoorlie.
mineral
Magnetite
A naturally magnetic black iron oxide and a major iron ore; strongly magnetic specimens are known as lodestone.
mineralGraveyard Point Agate
A celebrated plume agate from the Oregon-Idaho border, known for dramatic black, gold, and red plumes in clear chalcedony.
gemstone
Pyrargyrite
A silver antimony sulfosalt known as dark ruby silver, an important silver ore with deep red internal reflections.
mineralMorrisonite Jasper
A rare, prized Oregon picture jasper known for blue-green orbs and scenic patterns, often called the king of jaspers.
mineral
Stephanite
A black metallic silver antimony sulfide, historically a notable silver ore known as brittle silver ore.
mineral
Zincite
A rare zinc oxide best known for its deep red to orange color, classically from Franklin, New Jersey, and as colorful man-made crystals.
mineral