Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Pumpkin Obsidian
An orange-to-rust colored variety of natural volcanic glass whose warm tone comes from iron oxide staining within the obsidian.
igneous
Ruin Marble
A fractured fine-grained limestone whose iron-stained crack networks form natural scenes resembling ruined cities and landscapes.
sedimentary
Landscape Opal
A common opal containing dendritic or mossy mineral inclusions that form miniature landscape-like scenes inside the stone.
gemstone
Dendritic Opal
A common opal with branching, tree-like mineral inclusions that create natural fern, moss, or landscape patterns.
gemstone
Yellow Agate
A yellow to golden banded chalcedony colored by iron, ranging from natural honey tones to dyed commercial stones.
gemstone
Red Agate
A red-toned banded chalcedony colored by iron oxides, ranging from natural carnelian-like reds to heat-treated stones.
gemstone
Breccia
A coarse rock of angular, sharp-edged fragments cemented in a matrix, marking nearby rockfall, faulting, or impact.
sedimentary
Comendite
A peralkaline rhyolite, a silica-rich volcanic rock with excess alkalis, named for San Pietro Island's Comende district.
igneous
Brown Obsidian
Obsidian colored brown by iron oxide inclusions, frequently banded or swirled with black as in mahogany obsidian.
igneousOrange Obsidian
Obsidian colored orange by iron oxide inclusions; vivid uniform orange material is frequently manufactured glass rather than volcanic.
igneous
Geyserite
Porous opaline silica deposited around geysers and hot springs, often preserving delicate microbial textures.
sedimentaryHydroandradite
A hydrous, iron-rich garnet of the hydrogarnet group in which hydroxyl groups substitute for silica within the andradite structure.
mineral
Yellow Opal
A cheerful yellow opal ranging from translucent common opal to golden fire opal, colored by trace iron in the silica.
gemstoneTripolite
A soft, lightweight siliceous sedimentary rock made of fossil diatom remains, prized as a fine natural abrasive and polishing powder.
sedimentaryEulysite
A rare, dense iron-rich metamorphic rock composed of fayalite, iron pyroxene, and almandine garnet.
metamorphic
Quartzite
An extremely hard metamorphic rock formed from sandstone, made of fused quartz grains that break across rather than between the grains.
metamorphic
Novaculite
An extremely fine-grained, dense siliceous rock famous as Arkansas whetstone, prized for sharpening fine cutting tools.
sedimentaryEltyubyuite
A rare chlorine-bearing iron garnet-supergroup mineral, the ferric analogue of wadalite, formed in high-temperature combustion-metamorphic rocks.
mineral
Quartzite Sandstone
A tough, quartz-rich sandstone cemented by silica, transitional toward true quartzite but still sedimentary in origin.
sedimentary
Opal
A hydrated silica gemstone famous for its shimmering play-of-color, ranging from white and black opal to fiery orange fire opal.
gemstone
Silcrete
Extremely hard surface rock formed when silica cements soil and sediment into a tough duricrust in arid landscapes.
sedimentary
Wood Opal
Fossil wood replaced by opaline silica that preserves wood grain, occasionally showing the play-of-color of precious opal.
gemstone
Blue Quartz
A naturally blue quartz colored by tiny mineral inclusions such as dumortierite or scattered rutile and tourmaline fibers.
crystal
Tholeiitic Basalt
The most abundant basalt type on Earth, a silica-saturated subalkaline lava that forms ocean crust and flood basalts.
igneous