Rock & Mineral Encyclopedia

Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.

Breccia

A coarse rock of angular, sharp-edged fragments cemented in a matrix, marking nearby rockfall, faulting, or impact.

A vivid green hydrous nickel-magnesium silicate that is a major ore of nickel, mined from weathered ultramafic rocks.

Hard surface crust formed when iron oxides cement soil and sediment into a rusty, durable duricrust in tropical and weathered terrains.

An iron-rich sedimentary rock, often heavy and rusty-weathering, historically mined as a major source of iron ore.

Agate that was shattered and naturally re-cemented by silica, creating a mosaic of angular fragments in a quartz matrix.

A chromium-rich pyrope garnet whose intense blood-red color comes from chromium, often mined from ant hills and kimberlite weathering.

A rare breccia formed by meteorite impact, containing shocked rock fragments and glassy melt blobs welded together.

A jasper made of angular fragments naturally cemented back together, typically showing red and brown pieces in a quartz matrix.

A cohesive fault rock formed by brittle crushing and grinding of rock along a fault zone, with angular fragments in a fine matrix.

A fine-grained clastic rock of silt-sized grains, intermediate between sandstone and mudstone, with a gritty feel.

A fossiliferous jasper packed with spiral snail shells, technically a silicified gastropod limestone from Wyoming.

A metamorphic rock of calcium-rich silicate minerals formed from impure limestone or dolomite altered by heat and fluids.

A calcium-magnesium tourmaline that forms in metamorphosed limestones, typically dark green to brown and often in well-formed crystals.