Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Crowley Ridge Agate
Agate found in the gravels of Crowley's Ridge in northeastern Arkansas, a stream-transported banded chalcedony.
gemstone
Cobaltite
A silver-white cobalt arsenic sulfide that is a leading ore of cobalt, forming bright metallic cubic and pyritohedral crystals.
mineralMadupite
A rare ultrapotassic lamproite rich in phlogopite mica and diopside, classically from the Leucite Hills of Wyoming.
igneous
Pinfire Opal
A precious opal pattern made of tiny, densely packed pinpoint flashes of play-of-color, like sparkling speckles across the stone.
gemstone
Celsian
A rare barium-rich feldspar that forms in manganese and barium-enriched metamorphic and hydrothermal deposits, the barium end-member of the feldspar family.
mineral
Blue Sapphire
The blue gem variety of corundum, prized for its rich color, extreme hardness, and brilliance second only to diamond.
gemstone
Monazite
A reddish-brown rare-earth phosphate that is a primary ore of cerium, thorium and other rare-earth elements, often found in placer sands.
mineral
Oligoclase
A sodium-rich plagioclase feldspar between albite and andesine, parent of aventurescent sunstone and the bluish gem peristerite.
mineral
Conglomerate
A coarse sedimentary rock of rounded pebbles and gravel cemented in a finer matrix, recording ancient rivers and beaches.
sedimentary
Calc-Silicate Rock
A metamorphic rock of calcium-rich silicate minerals formed from impure limestone or dolomite altered by heat and fluids.
metamorphicDragon Blood Jasper
A green-and-red ornamental stone of epidote and red piemontite or iron oxide, named for its dragon-skin coloring; not a true jasper.
metamorphicLace Obsidian
Black volcanic glass laced with delicate web-like veins of contrasting color, formed by flow banding and fine crystallization.
igneous
Nephrite
One of the two jade minerals, an amphibole prized for its extreme toughness and soft, waxy green hues used in carving for millennia.
gemstone
Emerald Green Tourmaline
A richly saturated green variety of elbaite tourmaline whose color rivals emerald, colored by trace iron, chromium, or vanadium.
gemstoneLotus Garnet
A delicate pinkish-purple to peach garnet from Tanzania, a pyrope-spessartine blend named for the soft colors of a lotus flower.
gemstone
Arkose
A coarse, feldspar-rich sandstone, often pink, that records rapid erosion of granitic source rock under arid conditions.
sedimentary
Calcarenite
Sand-grained limestone composed of carbonate particles such as shell fragments and ooids cemented into a calcite rock.
sedimentaryScenic Agate
A translucent agate whose mineral inclusions resemble miniature landscapes of trees, hills, and horizons within the stone.
gemstone
Chocolate Opal
Precious opal with a warm chocolate-brown body tone that makes its rainbow play-of-color glow, mainly from Ethiopia and Mexico.
gemstone
Feldspathic Sandstone
A feldspar-rich sandstone, often pink, that points to granitic source rocks eroded quickly in dry or cold climates.
sedimentary
Tiger Iron
A banded combination rock of golden tiger's eye, red jasper, and metallic hematite, formed in ancient iron deposits.
metamorphicTri-Color Tourmaline
Tourmaline displaying three distinct color zones in a single crystal, a striking natural result of changing growth chemistry.
gemstoneQuartz Arenite
A clean, mature sandstone made almost entirely of quartz grains, representing extreme weathering, sorting, and recycling of sediment.
sedimentary
Cat's Eye Pink Tourmaline
Pink tourmaline cut en cabochon to reveal a moving band of light, a phenomenal gem colored by manganese with parallel inclusions.
gemstone