Rock & Mineral Encyclopedia

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

Foitite

A rare alkali-deficient tourmaline whose X crystal site is largely vacant, giving slender dark blue to bluish-black crystals.

A natural sheen obsidian showing a warm gold shimmer plus peacock iridescence, caused by aligned nanoparticle layers within black glass.

A vivid yellow-and-black banded stone from Indonesian volcanic vents, colored by sulfur, arsenic minerals and iron oxides, not true jasper.

A graded sedimentary deposit laid down by underwater turbidity currents, recording avalanches of sediment cascading down submarine slopes.

A jasper crossed by fine dark veins forming a spiderweb-like network, often a brecciated stone cemented by darker matrix.

A banded agate whose internal structures resemble cathedral spires, arches, or a city skyline of towers and pinnacles.

A rare agate that forms naturally with flat polygonal faces and angular geometric shapes rather than the usual rounded nodule.

A blue-violet zoisite found only in Tanzania, famous for its vivid trichroic color and rarity.

A fine-grained, low-grade metamorphic rock that splits into flat sheets along slaty cleavage, long used for roofing and flooring.

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

A brown fossiliferous chalcedony packed with spiral freshwater snail shells, technically agatized fossil rock from Wyoming.

Quartz with a stepped, multi-pointed structure of parallel side crystals resembling the spires of a cathedral.

A classic Oregon plume agate from the Priday Ranch beds, showing feathery mineral plumes suspended in translucent chalcedony.

A chromium-dominant tourmaline related to dravite, producing intensely deep green to blackish-green crystals from chromium-rich metamorphic rocks.

A fine-grained sedimentary rock of compacted clay and silt that, unlike shale, breaks in blocks rather than thin layers.