Rock & Mineral Encyclopedia
Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.
Fossiliferous Limestone
Calcium-carbonate sedimentary rock packed with visible fossils, recording ancient marine life within an easily scratched, fizzing matrix.
sedimentary
Knorringite
A chromium-rich magnesium garnet of the pyrope series that crystallizes in the deep mantle and is a valuable diamond indicator mineral.
mineral
Lamproite
A rare ultrapotassic, magnesium-rich volcanic rock from deep in the mantle, famous as the diamond host at Argyle in Australia.
igneous
Shell Opal
Fossil shells whose original material has been replaced by opal, preserving ancient marine forms in common or precious opal.
gemstone
Pink Obsidian
A pink to rose volcanic glass; some is natural iron-tinted obsidian while much sold commercially is color-treated glass.
igneous
Blue Obsidian
Blue-colored volcanic glass; genuine natural blue obsidian is very rare, while much blue obsidian on the market is manufactured glass.
crystal
Emerald Green Obsidian
A bright emerald-green glass sold as obsidian; saturated transparent green is manufactured, while rare natural green obsidian is only faintly tinted.
igneous
Pink Lady Obsidian
Obsidian showing a pink-to-rose sheen or hue; natural examples get color from interference effects, while uniform pink material is often manufactured glass.
igneous