Opalized Fossil (Shell Opal)
Image: <a href="//commons.wikimedia.org/wiki/User:Archaeodontosaurus" title="User:Archaeodontosaurus">Didier Descouens</a> (CC BY-SA 3.0)
Mineral NameOpalized Fossil (Shell Opal)
Chemical FormulaSiO2·nH2O
Mohs Hardness6
Crystal Systemamorphous
Lustervitreous
Streak Colorwhite
Cleavagenone
Fractureconchoidal
Specific Gravity2.1
Colorswhite, cream, iridescent (green, pink, red, blue)
Transparencytranslucent
Type LocalityQueensland, Australia
Mineral GroupSilicates (mineraloid)
Usesjewelry, collector
Associated Mineralssandstone, claystone, ironstone
Rarityuncommon
Description
A cluster of fossilized bivalve and gastropod shells, completely replaced by precious opal, exhibiting a vibrant play-of-color within a greyish sedimentary matrix.
Geological Context
Opalized fossils form when silica-rich solutions infiltrate porous sedimentary rocks, replacing organic material like shells or wood over millions of years. In Queensland, Australia, these are typically found in Cretaceous sediments, where ancient inland seas provided the conditions for silica deposition.
