Rock & Mineral Encyclopedia

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

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Fossil shells whose original material has been replaced by opal, preserving ancient marine forms in common or precious opal.

Fossil material whose original substance has been replaced by opal, preserving ancient shapes in common or play-of-color opal.

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

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

Soft, lightweight siliceous rock made of fossilized diatom shells, valued as a filter, abrasive, and absorbent.

Ancient wood whose organic tissue has been replaced by silica, preserving the grain, rings, and structure of the original tree in stone.

A soft, lightweight, chalky sedimentary rock made of the silica shells of microscopic diatoms, prized for its absorbency and filtering ability.

A soft, lightweight siliceous sedimentary rock made of fossil diatom remains, prized as a fine natural abrasive and polishing powder.

Calcium-carbonate sedimentary rock packed with visible fossils, recording ancient marine life within an easily scratched, fizzing matrix.

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

Fossilized wood in which the original organic structure has been replaced by opal, sometimes showing precious play-of-color.

A common opal containing moss- or fern-like mineral inclusions that resemble plants suspended in a pale silica body.

A jasper marked with soft feather- or plume-like mineral inclusions that drift through a pale silica body.