Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Cat'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
Yowah Nut Opal
Small ironstone concretions from Yowah, Queensland, whose hollow or veined centers hold brilliant precious boulder opal.
gemstone
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
Fire Obsidian
A rare obsidian showing brilliant fiery iridescence caused by thin nanolayers of magnetite crystals diffracting light within the glass.
crystal
Fire Agate
A rare brown chalcedony containing thin iron-oxide layers that produce flashing, fiery rainbow iridescence like trapped flames.
gemstone
Jelly Opal
A translucent, gelatinous-looking opal whose transparency gives floating, glowing play-of-color a watery, jelly-like appearance.
gemstone
Water Opal
A transparent, colorless opal that looks like water or jelly, sometimes flashing subtle play-of-color from within.
gemstone
Star Opal
Opal that displays a radiating, star-shaped pattern of play-of-color, a rare and prized internal structure.
gemstone
Ice Opal
A clear, glassy, near-colorless opal resembling ice, sometimes with subtle internal flashes of play-of-color.
gemstone
Hydrophane Opal
A porous opal, typified by Ethiopian Welo, that absorbs water and temporarily becomes more transparent or changes appearance until it dries.
gemstone
Bone Opal
Fossil bone in which opal has replaced the original tissue, sometimes showing play-of-color, a rare collector fossil.
gemstone
Opalite
A man-made opalescent glass that glows milky blue in reflected light and warm orange when backlit, often sold as a crystal.
crystal
Fireworks Obsidian
Black volcanic glass dotted with radiating spherulite bursts that look like exploding fireworks frozen in the stone.
igneous
Turquoise
A prized blue to blue-green copper-aluminium phosphate, often veined with dark matrix, treasured for jewelry across many cultures.
mineral
Wacke
A poorly sorted, muddy sandstone with abundant clay matrix between its grains, typically dark and deposited by turbidity currents.
sedimentary
Spiderweb Jasper
A jasper crossed by fine dark veins forming a spiderweb-like network, often a brecciated stone cemented by darker matrix.
mineral
Flame Agate
A chalcedony agate with red, orange, and yellow plume or banding patterns that rise like dancing flames within the stone.
gemstone
Flame Jasper
A fiery jasper whose red, orange, and yellow plumes lick across the stone like flames against an earthy background.
mineral
Emerald Crystal
The natural crystalline form of emerald, the prized green chromium-and-vanadium variety of beryl and the May birthstone.
crystal
Flint
A hard, dark variety of chert that knaps into razor-sharp edges and sparks against steel, central to Stone Age technology.
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
Sunset Tourmaline
A warm-hued tourmaline blending orange, pink and red tones reminiscent of a sunset sky.
gemstone
Tiger Iron
A banded combination rock of golden tiger's eye, red jasper, and metallic hematite, formed in ancient iron deposits.
metamorphic