Rock & Mineral Encyclopedia

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

Bone 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.

Fossil shells whose original material has been replaced by opal, preserving ancient marine forms in common or precious opal.

Fossil material whose original substance has been replaced by opal, preserving ancient shapes in common or play-of-color opal.