Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Double Flow Obsidian
Obsidian formed from two merged lava flows, producing a stone with two distinct bands of sheen or color.
igneousWehrite
An ultramafic rock of olivine and clinopyroxene, a peridotite variety common as cumulate layers in mafic intrusions.
igneous
Chlorite Schist
A soft, green, foliated rock rich in chlorite, formed by low-grade metamorphism of mafic or volcanic rocks.
metamorphicFlame Obsidian
Black volcanic glass that flashes flame-like bands of iridescent color when light strikes aligned nanoscale inclusions.
igneous
Hawk's Eye
The blue-grey relative of tiger's eye, a chatoyant quartz showing a shifting band of light like a bird of prey's eye.
gemstoneCat's Eye Morganite
Pink beryl (morganite) that shows chatoyancy, a moving band of light, when cut as a cabochon, thanks to parallel tube inclusions.
gemstone
Graphic Feldspar
A pegmatite rock of feldspar intergrown with wedge-shaped quartz that resembles ancient runic or Hebrew writing.
igneous
Talc Schist
An extremely soft, soapy-feeling foliated rock made largely of talc, formed by metamorphism of magnesium-rich rocks.
metamorphicDiatomaceous Earth
Soft, lightweight siliceous rock made of fossilized diatom shells, valued as a filter, abrasive, and absorbent.
sedimentary
Teepee Canyon Agate
A fortification agate from the Black Hills of South Dakota, known for tight, colorful banding closely related to the famous Fairburn agate.
gemstoneMarl
A soft, earthy sedimentary rock made of a mixture of calcium carbonate and clay, intermediate between limestone and mudstone.
sedimentaryCat's Eye Opal
An opal cut to show chatoyancy, a sharp moving band of light like a cat's eye, usually in honey, green or yellow common opal.
gemstone
Metaquartzite
A hard, tough metamorphic rock of fused quartz grains, formed by recrystallizing quartz sandstone under heat and pressure.
metamorphic
Turritella Agate
A brown fossiliferous chalcedony packed with spiral freshwater snail shells, technically agatized fossil rock from Wyoming.
sedimentary
Suevite
A rare breccia formed by meteorite impact, containing shocked rock fragments and glassy melt blobs welded together.
metamorphic
Novaculite
An extremely fine-grained, dense siliceous rock famous as Arkansas whetstone, prized for sharpening fine cutting tools.
sedimentary
Orthoclase
A common rock-forming potassium feldspar, the Mohs hardness reference at 6, found in granites and used in ceramics and glassmaking.
mineral
Ruby in Zoisite
A striking rock of green zoisite studded with red-pink ruby crystals and black hornblende, also called anyolite.
metamorphic
Silcrete
Extremely hard surface rock formed when silica cements soil and sediment into a tough duricrust in arid landscapes.
sedimentary
Albite
The sodium end-member of the plagioclase feldspar series, a common white rock-forming mineral and parent of peristerite moonstone.
mineral
Anthracite
The highest-rank coal, a hard, lustrous black rock that burns cleanly with little smoke and high heat output.
metamorphic
Calc-schist
A foliated metamorphic rock of calcite mixed with mica, quartz, and calc-silicate minerals, derived from marly sediments.
metamorphic
Lherzolite
The most common type of mantle peridotite, made of olivine with both orthopyroxene and clinopyroxene, representing fertile upper-mantle rock.
igneous
Lignite
The lowest rank of coal, a soft brown carbon-rich rock formed from compacted peat, used mainly for electricity generation.
sedimentary