10.6" Brilliant Red, Polished Dinosaur Bone (Gembone) Slab - Utah

Agatized or agate replaced dinosaur bone is a rare form of fossilized dinosaur bone where the original fossilized bone, typically permineralized with calcite, has been re-mineralized with silica-type compounds such as agate, jasper, chalcedony, or opal.

In a unique and isolated circumstance, the strata on the Colorado Plateau were uplifted during the tertiary intrusions about 35 million years ago when the San Rafael Swell and the La Sals, Henry, and Abajo Mountains were formed. As these ranges were forming, local strata layers were flooded with silica-rich, superheated groundwater. This provided the appropriate environment to start this calcite-silicate replacement in the original fossils. The most prolific layers of gem bone come from the Morrison Formation, which is late Jurassic in age.