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Fossil shells whose original material has been replaced by opal, preserving ancient marine forms in common or precious opal.

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

A common potassium feldspar identical in composition to orthoclase but more ordered, famous for its green gem variety amazonite.