Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Dravite
The magnesium-rich brown member of the tourmaline group, named for Austria's Drava River and prized for warm earthy tones.
mineral
Trachyte
A fine-grained volcanic rock dominated by alkali feldspar, the extrusive equivalent of syenite.
igneous
Starburst Agate
Agate containing radiating sprays of mineral needles that fan out like bursting stars within the chalcedony.
gemstone
Pelitic Schist
A schist derived from clay-rich sediments, rich in mica and often bearing index minerals like garnet, staurolite, or kyanite.
metamorphic
Paintbrush Agate
A plume agate whose inclusions form upright, bristly clusters resembling the strokes of a paintbrush.
gemstone
Holley Blue Agate
A rare translucent lavender-blue agate from the Holley area of Oregon, prized for its soft purple-blue color.
gemstone
Crowley Ridge Agate
Agate found in the gravels of Crowley's Ridge in northeastern Arkansas, a stream-transported banded chalcedony.
gemstone
Brecciated Agate
Agate that was shattered and naturally re-cemented by silica, creating a mosaic of angular fragments in a quartz matrix.
gemstone
Blue Chalcedony
A translucent, soft blue variety of microcrystalline quartz whose color comes from light scattering through its fine structure.
mineral
Blood Agate
A deep red banded agate colored by iron oxides, valued as a vivid red lapidary and jewelry stone.
gemstone
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
Shale
The most common sedimentary rock, a fissile mudrock of compacted clay and silt that splits into thin layers.
sedimentary
Greywacke
A hard, dark, poorly sorted sandstone with a muddy matrix, typically deposited by underwater turbidity currents.
sedimentary
Zebra Agate
A banded chalcedony agate with bold alternating dark and light stripes resembling zebra markings, sometimes color-enhanced.
gemstone
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.
gemstone
Sunset Agate
A warmly colored chalcedony agate with reds, oranges, golds, and pinks that blend like the glowing bands of a sunset sky.
gemstone
Slate
A fine-grained, low-grade metamorphic rock that splits into flat sheets along slaty cleavage, long used for roofing and flooring.
metamorphic
Shadow Agate
A banded agate that displays a moving shadow or flash across its surface when tilted under light, caused by closely spaced parallel bands.
gemstone
Polyhedroid Agate
A rare agate that forms naturally with flat polygonal faces and angular geometric shapes rather than the usual rounded nodule.
gemstone
Phyllite
A fine-grained foliated metamorphic rock between slate and schist, recognized by its silky silvery sheen and wavy, crinkled surfaces.
metamorphic
Honey Agate
A warm golden to amber translucent chalcedony agate whose color and glow resemble honey, sometimes with banding.
gemstone
Graphite Schist
A dark, foliated schist rich in graphite that leaves a grey-black mark and forms from metamorphosed carbon-rich sediments.
metamorphic
Frost Agate
A pale chalcedony agate with cloudy, frost-like white patterning suggesting frost on a window or icy crystalline textures.
gemstone
Flame Agate
A chalcedony agate with red, orange, and yellow plume or banding patterns that rise like dancing flames within the stone.
gemstone