Shark teeth are one of the most fascinating finds on the beach. Their striking black color and razor-sharp serrated edges make them unmistakable, even to the casual beachcomber. But why are shark teeth black when you first find them, and how do they get their dark coloring? Understanding the composition and fossilization of shark teeth sheds some light on this mysteriously dark dental phenomenon.
Shark teeth are commonly found washed up on beaches around the world, especially near areas where sharks are abundant. Most shark teeth are black, gray, or brown when initially found, though some types of teeth may appear milky white. The dark coloration is a result of the tooth composition and the process by which the teeth become fossilized over time.
Shark teeth are composed of osteodont tissue, a calcified material similar to bone and dentin. However, shark teeth also contain high levels of minerals like iron and magnesium. It is these mineral deposits that contribute to the dark shades of black, brown, and gray.
As shark teeth get buried in sediment and fossilize over thousands of years, the iron and magnesium undergo chemical changes. Iron will react with sulfur compounds, forming the black iron sulfide mineral pyrite, also known as fool’s gold. Magnesium interacts with other minerals like phosphates and carbonates to create dark gray or brown compounds.
The coastal environment where fossils form also affects tooth color. Teeth buried in low oxygen environments will darken more over time. Teeth preserved in phosphatic sediments may turn black as pyrite forms around bone collagen. The minerals that permeate the porous tooth surface through fossilization result in darker fossil shark teeth.
Shark Tooth Composition
Shark teeth are composed of a bonelike material called osteodont. This gives them strength and hardness to grab slippery prey and saw through tough hide and flesh. Here is an overview of the materials that make up a shark tooth:
| Material | Role |
|---|---|
| Hydroxyapatite | A mineral form of calcium phosphate, gives hardness |
| Collagen | Fibrous protein, provides elasticity |
| Dentin | Bony tissue under enamel, supports crown |
| Pulp | Soft tissue with nerves and blood vessels |
| Enamel | Hardest outer cap of tooth crown |
Shark teeth also contain higher mineral content than human teeth, especially iron and magnesium. Iron concentrations are around 60 parts per million compared to only 2 ppm in humans. Magnesium can be over 50 times higher in shark teeth. These minerals contribute to the dark coloration.
Fossilization and Color Change
After a shark loses a tooth, it settles on the seafloor where fossilization begins. Over time, the collagen breaks down and minerals seep into the pore spaces. The iron and magnesium undergo chemical changes during this process:
- Iron reacts with sulfur compounds to produce pyrite, turning teeth black.
- Magnesium forms new gray/brown compounds with carbonate and phosphate.
- Low oxygen environments increase pyrite formation and darkening.
- Phosphatic sediments turn teeth black as pyrite forms around collagen.
It takes thousands to millions of years for fossils to fully form. The longer the tooth is buried, the more minerals replace collagen, and the darker the tooth’s color becomes. Shark teeth found soon after falling out may still appear white from enamel, but fossilized teeth are almost always blackened.
Tooth Color Based on Shark Species
While most fossil shark teeth are dark colored, different shark species have teeth with characteristic colors and textures. Here are some of the more common shades and patterns:
| Shark | Tooth Color |
|---|---|
| Great White | Black or gray with serrated cutting edges |
| Tiger Shark | Dark gray with distinct horizontals lines |
| Bull Shark | Shiny black with worn triangular tips |
| Mako | Black and incredibly pointy |
| Hammerhead | Dark brown with notched edges |
Fossilized megoladon teeth can be over 7 inches long and are typically black or gray. Large teeth from prehistoric sharks like Carcharocles megalodon are prized finds for collectors.
Cleaning and Whitening Shark Teeth
Freshly discovered shark teeth may still have sediment, dirt, or grime stuck to the surface. Gently scrubbing with a soft brush under running water can help dislodge debris. Here are some tips for cleaning and whitening shark teeth:
- Brush gently with toothbrush and water to remove sediment
- Soak in vinegar solution to dissolve calcium deposits
- Use baking soda abrasive paste with soft brush
- Avoid bleach or harsh chemicals that may damage enamel
- Once clean, peroxide solution can whiten and brighten
- For display, coat with mineral oil to bring out contrast
While cleaning may lighten shark teeth somewhat, the inherent dark minerals mean that most fossils will retain a gray, brown, or black shade even after scrubbing and whitening techniques.
Finding and Collecting Shark Teeth
Shark teeth can often be found washed up on beaches near areas with abundant shark populations. Places to search include:
- East and Gulf Coast beaches of North America
- Coastal areas throughout Florida
- Beaches near river mouths worldwide
- Coastlines along the Mid-Atlantic Ridge
Look for black triangular shapes in the sand just at or above the high tide line. Search after strong storms or aggressive wave action churn up more fossils. Joining local shark tooth hunting clubs and fossil groups can provide community and advice.
When collecting shark teeth, be sure to keep the following tips in mind:
- Verify regulations and get permits for collecting fossils on beaches
- Only collect teeth lying loose, don’t dig out jaws from fossils
- Photograph specimens before removing from site
- Handle carefully to avoid damage
- Record detailed notes on tooth location and environment
Responsible collecting helps preserve shark tooth fossils for future study and appreciation.
Conclusion
Shark teeth get their signature black coloration through high mineral content and the process of fossilization over millennia. The initial osteodont composition and enrichment with iron and magnesium set the stage for teeth to turn dark as they mineralize into fossils. Chemical changes create black pyrite and other compounds that permeate and darken the porous tooth structure. Understanding the biology and chemistry behind this phenomenon provides insight into these striking and mysterious dental fossils.