Opalized Plesiosaur Fossil
Image: James St. John (CC BY 2.0)
Mineral NameOpalized Plesiosaur Fossil
Chemical FormulaSiO2·nH2O
Mohs Hardness5.5
Crystal Systemamorphous
Lustervitreous
Streak Colorwhite
Cleavagenone
Fractureconchoidal
Specific Gravity2.1
Colorswhite, tan, brown, blue, green, purple, orange, red
Transparencytranslucent
Type LocalityAustralia
Mineral GroupSilicates (mineraloid)
Usescollector, scientific study
Rarityvery-rare
Description
This specimen is an opalized plesiosaur vertebra, displaying a base color of light tan to brown with vibrant flashes of iridescent blue, green, purple, orange, and red play-of-color across its surface.
Geological Context
Opalized fossils form when silica-rich waters permeate porous organic material, such as bone, and deposit amorphous silica (opal) over long periods, replacing the original structure. This process typically occurs in sedimentary environments where conditions are favorable for opal formation.
