Odontolite

What is odontolite?

Odontolite, also known as bone turquoise or fossil turquoise, is a fossil bone or tooth that has been mineralized.¹²

It is composed of the phosphate mineral apatite, which acquires a distinct blue coloration due to the presence of vivianite, a hydrated iron phosphate. While odontolite bears a visual resemblance to turquoise, the two can be distinguished through chemical analysis.¹²

How does vivianite give fossils a blue color?

Vivianite is a hydrated iron phosphate mineral that acts as a coloring agent in fossils, such as odontolite. When freshly exposed, the mineral is colorless; however, its color changes significantly upon exposure to air due to the oxidation of its iron content.⁴⁵

As the iron within the vivianite oxidizes, the mineral transitions through various shades, including light green, blue-green, dark blue, or even black, depending on the duration of exposure. This chemical process is similar to how the oxidation state of iron influences the color of other materials, such as the browning of meat when iron in myoglobin oxidizes over time. In the context of fossils, this oxidation of iron-rich vivianite deposits is what imparts the characteristic blue hue to the bone or tooth material.⁴⁶

What is the difference between real turquoise and bone turquoise?

While bone turquoise (also known as odontolite) visually resembles turquoise, the two are fundamentally different in origin and composition.

• Composition: True turquoise is a hydrated phosphate of copper and aluminum. In contrast, bone turquoise is a fossil bone or tooth composed of the phosphate mineral apatite.¹
• Coloration: The blue color in bone turquoise is caused by the presence of vivianite, an iron phosphate, which mineralizes the fossilized remains.²¹
• Identification: Although they look similar, they can be distinguished through chemical analysis, as their elemental makeup is distinct.¹

What is the process of fossilization for bones and teeth?

The process of fossilization for bones and teeth typically begins with the death of an organism followed by rapid burial in sediment, which protects the remains from scavengers and slows decomposition. Because bones and teeth are solid and resistant, they are the most likely parts of an organism to be preserved.⁸⁹

Once buried, the remains undergo several potential transformations:

• Permineralization: Mineral-rich water seeps into the pores and interstices of the bone or tooth, depositing minerals like calcium carbonate or other salts, which turns the remains into stone.⁸⁹
• Mineralization (Replacement): The original skeletal material is completely dissolved and replaced by new mineral matter, creating a detailed stone replica of the original structure.⁸⁹
• Molding: In some instances, the original material is dissolved by circulating acidic solutions, leaving behind a cavity or mold that preserves the shape of the original bone or tooth.⁹¹⁰

These processes occur most effectively in water environments, where anaerobic conditions further aid in preserving fine details by preventing the activity of most organisms.⁹