Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Aquamarine Matrix
Aquamarine crystals still attached to their natural host rock, prized as mineral specimens showing beryl in its original pocket setting.
mineral
Emerald in Matrix
Natural emerald crystals still embedded in their host rock, prized as mineral specimens that show how the gem grew in place.
gemstone
Matrix Opal
Opal in which precious play-of-color is intimately dispersed through the pores of its host rock rather than forming a solid seam.
gemstone
Lithic Sandstone
A sandstone in which the dominant grains are fragments of pre-existing rocks rather than single minerals, signaling rapid erosion nearby.
sedimentary
Bone Opal
Fossil bone in which opal has replaced the original tissue, sometimes showing play-of-color, a rare collector fossil.
gemstone
Breccia
A coarse rock of angular, sharp-edged fragments cemented in a matrix, marking nearby rockfall, faulting, or impact.
sedimentary
Boulder Opal
Precious opal that forms in thin veins within brown ironstone boulders, cut with the host rock left as a natural dark backing.
gemstone
Cataclasite
A cohesive fault rock formed by brittle crushing and grinding of rock along a fault zone, with angular fragments in a fine matrix.
metamorphic
Greywacke
A hard, dark, poorly sorted sandstone with a muddy matrix, typically deposited by underwater turbidity currents.
sedimentary
Coquina
A soft, porous limestone made of loosely cemented shell and coral fragments, used as a coastal building stone.
sedimentary
Fossiliferous Limestone
Calcium-carbonate sedimentary rock packed with visible fossils, recording ancient marine life within an easily scratched, fizzing matrix.
sedimentary
Conglomerate
A coarse sedimentary rock of rounded pebbles and gravel cemented in a finer matrix, recording ancient rivers and beaches.
sedimentary
Tillite
A lithified glacial till, a poorly sorted rock of mixed boulders, pebbles and fine matrix that records ancient glaciations.
sedimentary
Banded Iron Formation
Ancient chemically deposited rock of alternating iron-oxide and silica bands recording Earth's early oxygenation and a major iron ore source.
sedimentary
Tiger Iron
A banded combination rock of golden tiger's eye, red jasper, and metallic hematite, formed in ancient iron deposits.
metamorphic
Kambaba Jasper
A dark green-and-black stromatolite jasper patterned with swirling orbs, formed from fossilized ancient microbial colonies.
sedimentary
Calcarenite
Sand-grained limestone composed of carbonate particles such as shell fragments and ooids cemented into a calcite rock.
sedimentary
Shelly Limestone
A limestone packed with visible shells and shell fragments, recording the accumulation of marine invertebrate remains on ancient sea floors.
sedimentary
Brecciated Agate
Agate that was shattered and naturally re-cemented by silica, creating a mosaic of angular fragments in a quartz matrix.
gemstone
Brecciated Jasper
A jasper made of angular fragments naturally cemented back together, typically showing red and brown pieces in a quartz matrix.
sedimentaryDiatomaceous Earth
Soft, lightweight siliceous rock made of fossilized diatom shells, valued as a filter, abrasive, and absorbent.
sedimentary
Orthoclase
A common rock-forming potassium feldspar, the Mohs hardness reference at 6, found in granites and used in ceramics and glassmaking.
mineral
Suevite
A rare breccia formed by meteorite impact, containing shocked rock fragments and glassy melt blobs welded together.
metamorphic
Smithsonite
Smithsonite is a zinc carbonate ore famous for glassy botryoidal crusts in blue-green, pink, and yellow hues.
mineral