Rock & Mineral Encyclopedia

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

Petrified Wood

Ancient wood whose organic tissue has been replaced by silica, preserving the grain, rings, and structure of the original tree in stone.

A rare, intensely blue chalcedony colored by copper-rich chrysocolla, prized as the most valuable of the blue chalcedonies.

Fossilized wood in which the original organic structure has been replaced by opal, sometimes showing precious play-of-color.

Fossil material whose original substance has been replaced by opal, preserving ancient shapes in common or play-of-color opal.