Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Calcrete
Carbonate-cemented soil crust formed in arid regions where calcium carbonate accumulates and hardens within the regolith.
sedimentary
Siderite
Siderite is an iron carbonate ore, a brown rhombohedral mineral of the calcite group found in sediments and veins.
mineral
Ruby
The red, chromium-colored variety of corundum, prized as one of the most valuable colored gemstones and second only to diamond in hardness.
gemstone
Bi-Color Tourmaline
Tourmaline displaying two distinct colors in a single crystal, a natural color-zoning effect that makes each stone unique.
gemstone
Lujavrite
A dark, layered agpaitic nepheline syenite rich in sodic pyroxene and amphibole with eudialyte, from the Lovozero and Ilimaussaq complexes.
igneousPeach Moonstone
A warm peach-to-apricot variety of moonstone feldspar showing a soft billowy sheen (adularescence) caused by internal light scattering.
gemstoneBekily Garnet
A rare color-change garnet from Bekily, Madagascar, shifting from bluish-green in daylight to purplish-red under warm light, including the famed blue garnets.
gemstone
Red Tourmaline
Vivid red to raspberry tourmaline, the most intense colors are marketed as rubellite, colored by manganese in the elbaite structure.
gemstone
Rainbow Tourmaline
Tourmaline showing many color zones in a single crystal, often revealing spectacular concentric patterns when sliced.
gemstone
Peat
A soft, spongy accumulation of partly decayed plant matter that forms in waterlogged bogs and is the first step toward coal.
sedimentary
Henritermierite
A rare manganese-bearing hydrogarnet notable for being tetragonal rather than cubic, found in metamorphosed manganese deposits in Morocco.
mineral
Dark Green Tourmaline
Deeply saturated green tourmaline colored by iron, often so dark it appears nearly black until viewed in bright light.
gemstone
Garnet
A group of silicate gemstones best known for deep red but spanning nearly every color, including green tsavorite and orange spessartine.
gemstone
Rainbow Opal
Precious opal that displays a broad, vivid sweep of spectral colors, flashing the full rainbow as it is tilted in the light.
gemstone
Yellow-Green Obsidian
A chartreuse yellow-green glass sold as obsidian; the bright color is manufactured and does not occur in natural volcanic glass.
igneousTeal Obsidian
A deep teal glass sold as obsidian; the saturated blue-green color is manufactured and not found in natural volcanic glass.
igneousChrome Spessartine
Chrome Spessartine is a rare chromium-bearing manganese garnet whose trace chromium intensifies its already vivid orange color.
gemstone
Chrome Tourmaline
An intensely green tourmaline colored by chromium and vanadium, prized for its vivid emerald-like color from East Africa.
gemstone
Pyromorphite
A lead phosphate secondary mineral known for barrel-shaped green to yellow crystals formed in oxidized lead deposits.
mineralMasasi Blue Garnet
Masasi Blue Garnet is a rare vanadium-bearing color-change garnet from Tanzania that appears blue-green by day and purplish-red indoors.
gemstone
Bog Iron
A soft, porous iron ore of limonite and goethite that forms in wetlands and bogs, historically the first iron source for many cultures.
sedimentary
Micrite
A very fine-grained limestone made of microcrystalline calcite mud, dense and smooth, deposited in calm carbonate settings.
sedimentary
Hyalite Opal
A clear, glassy, botryoidal common opal famous for its intense green fluorescence under UV light, caused by trace uranium.
gemstone
Dendritic Opal
A common opal with branching, tree-like mineral inclusions that create natural fern, moss, or landscape patterns.
gemstone