Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Calc-Silicate Rock
A metamorphic rock of calcium-rich silicate minerals formed from impure limestone or dolomite altered by heat and fluids.
metamorphic
Metabasalt
Basalt that has been metamorphosed, developing new minerals like chlorite, actinolite, and epidote that give it a greenish color.
metamorphic
Metaquartzite
A hard, tough metamorphic rock of fused quartz grains, formed by recrystallizing quartz sandstone under heat and pressure.
metamorphic
Cordierite Hornfels
A tough, fine-grained contact-metamorphic rock containing cordierite, often spotted, formed by heat from nearby igneous intrusions.
metamorphic
Sapropel
A soft, dark, organic-rich mud deposited in stagnant, oxygen-poor water, a key precursor to oil and gas source rocks.
sedimentary
Slate
A fine-grained, low-grade metamorphic rock that splits into flat sheets along slaty cleavage, long used for roofing and flooring.
metamorphic
Marble
A metamorphosed limestone of interlocking calcite crystals, prized for sculpture and architecture for its workability and polish.
metamorphic
Metarhyolite
Rhyolite that has been metamorphosed, recrystallizing its silica-rich volcanic material into a tougher felsic metamorphic rock.
metamorphic
Hornfels
A tough, fine-grained, non-foliated rock formed by the intense heat of nearby magma baking surrounding rock at contact zones.
metamorphic
Bituminous Shale
A dark, organic-rich shale loaded with kerogen and bitumen that can yield oil and gas, often finely laminated and combustible.
sedimentary
Whiteschist
A rare high-pressure metamorphic schist defined by the diagnostic assemblage of talc plus kyanite, often pale and silvery.
metamorphic
Chlorite Schist
A soft, green, foliated rock rich in chlorite, formed by low-grade metamorphism of mafic or volcanic rocks.
metamorphic
Phosphorite
Phosphate-rich sedimentary rock, the world's main source of phosphorus for fertilizers, formed in nutrient-rich marine settings.
sedimentary
Kambaba Jasper
A dark green-and-black stromatolite jasper patterned with swirling orbs, formed from fossilized ancient microbial colonies.
sedimentary
Black Shale
Dark, organic-rich fine-grained sedimentary rock formed in oxygen-poor waters, often a source rock for oil and gas.
sedimentary
Hyalophane
A barium-bearing potassium feldspar intermediate between orthoclase and celsian, found in barium-rich metamorphic and ore deposits.
mineral
Quartzite
An extremely hard metamorphic rock formed from sandstone, made of fused quartz grains that break across rather than between the grains.
metamorphic
Oil Shale
A fine-grained sedimentary rock rich in solid organic matter (kerogen) that yields oil and gas when heated.
sedimentary
Green Marble
A green ornamental stone, often serpentine-rich marble or verde antique, valued for its rich green color and white veining.
metamorphic
Verdite
A rich green, fuchsite-rich metamorphic rock from southern Africa, prized as a carving and ornamental stone.
metamorphic
Limestone
A soft carbonate sedimentary rock made mostly of calcite, often packed with marine fossils and prone to forming caves.
sedimentary
Coal
A combustible black sedimentary rock formed from ancient plant matter and burned for centuries as a primary fossil fuel.
sedimentary
Mudstone
A fine-grained sedimentary rock of compacted clay and silt that, unlike shale, breaks in blocks rather than thin layers.
sedimentary
Siltstone
A fine-grained clastic rock of silt-sized grains, intermediate between sandstone and mudstone, with a gritty feel.
sedimentary