Rock & Mineral Encyclopedia

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

Fossil Opal

Fossil material whose original substance has been replaced by opal, preserving ancient shapes in common or play-of-color opal.

Fossilized wood in which the original organic structure has been replaced by opal, sometimes showing precious play-of-color.

Fossil shells whose original material has been replaced by opal, preserving ancient marine forms in common or precious opal.

Fossil bone in which opal has replaced the original tissue, sometimes showing play-of-color, a rare collector fossil.

Fossil wood replaced by opaline silica that preserves wood grain, occasionally showing the play-of-color of precious opal.

Ancient wood whose organic tissue has been replaced by silica, preserving the grain, rings, and structure of the original tree in stone.