Introduction: Why Fossil Shark Teeth Are Different Colors

One of the first things people notice about fossil shark teeth is their incredible variety of colors. Many fossil shark teeth are jet black, however, others can be red, orange, brown, blue, gray, green, or even white. Many people assume the color tells you how old the tooth is or what species of shark it came from, but that is usually not the case.

In reality, the color of a fossil shark tooth is determined mostly by the sediment and minerals surrounding it during fossilization. In other words, the environment where the tooth was buried is what gives it its final color.

When a shark loses a tooth, it sinks to the ocean floor and becomes buried in mud, sand, clay, or gravel. Over thousands or even millions of years, groundwater carrying dissolved minerals slowly moves through the sediment and into the tooth. During this fossilization process, minerals from the surrounding sediment replace much of the tooth’s original material.

Why are most fossil shark teeth black? The simple answer is that phosphate is extremely common in many marine fossil deposits, and over time it replaces the original material in the tooth, turning it black. This is why black fossil shark teeth are found so commonly around the world.

However, phosphate is only part of the story. Different minerals can produce many different colors. Iron-rich sediments may turn fossil shark teeth red, orange, or brown, while other mineral combinations can create blue, gray, green, or tan teeth. Even two teeth from the same species can end up completely different colors if they fossilized in different environments.

Because of this, fossil shark tooth colors can tell us a surprising amount about the ancient sediments and environments where the teeth were preserved. In some cases, fossil collectors can even identify the type of deposit, or formation, a tooth came from simply by looking at its color.

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Why Fossil Shark Teeth Are Not Always the Same Color (Roots, Enamel, and Other Factors)

At first glance, the color of fossil shark teeth seems simple: the surrounding sediment determines the color of the tooth. While this is generally true, fossil shark teeth are often much more complicated than that.

If you have spent any time collecting fossil shark teeth, you have probably noticed that many teeth do not match the “basic explanation.” Some teeth have black roots and gray enamel. Others are streaked, spotted, speckled, or even multicolored. Blue and green teeth may appear in gray sediment, while white teeth can sometimes be found in dark brown layers.

The reason is that fossil shark tooth color is controlled by many factors, not just one single mineral. The chemistry of the tooth itself, the surrounding sediment, groundwater movement, and even plant roots can all influence the final appearance of the fossil.

One of the most important processes behind these changes is diagenesis, which is the set of physical, chemical, and biological changes that occur after a tooth is buried in sediment and becomes a fossil. During diagenesis, minerals from groundwater can replace parts of the original tooth material, stain the fossil different colors, or alter the contrast between the enamel and root.

Because diagenesis does not happen uniformly, even teeth buried in the same layer can experience very different chemical changes, helping explain why fossil shark teeth often show such a wide range of colors and patterns.

To better understand why fossil shark teeth can vary so much in appearance, it helps to break the process down into a few common causes.

Why are shark tooth roots and enamel often different colors?

One of the most common questions collectors ask is why the root and enamel of a fossil shark tooth are often different colors.

The answer comes down to chemistry. The enamel and root are made from different materials and do not fossilize in exactly the same way. The porous root tends to absorb minerals more easily, while the enamel is denser and more resistant to chemical change.

Because of this, minerals in the sediment may darken or replace the root faster than the enamel. This is why many fossil shark teeth have black roots with lighter gray, blue, or tan enamel.

In some cases, the difference can be dramatic, creating sharp color contrasts between the root and crown of the tooth.

Why are fossil shark teeth in the same layer not the same color?

Even fossil shark teeth found in the exact same layer are not always the same color. For example, collectors in Aurora, North Carolina often find yellow-green shark teeth in light gray sediment, while nearby teeth may be dark gray or black.

This happens because fossilization chemistry can vary greatly over very small distances. Different sediments interact with fossils in different ways. Clay behaves differently than sand, silt, or limestone, and each type of sediment contains different minerals and organic material.

Other environmental factors also play a role. Organic-rich sediment may darken a tooth, while more oxygen-rich conditions can produce lighter colors. The pH of the sediment, whether acidic or alkaline, also affects how minerals enter and replace the original tooth.

Even the size of the sediment grains can influence fossil color by changing how groundwater moves through the deposit. All of these small differences help explain why fossil shark teeth can vary so much in color, even when they are found side by side.

Color changes after fossilization (groundwater, tree roots, and other factors)

Many people assume a fossil shark tooth keeps the same color forever once it fossilizes, but that is not always true. Fossil shark teeth can continue to change color long after the fossilization process is complete.

Groundwater, plant roots, cracks in the sediment, and changing soil chemistry can all alter the appearance of a fossil tooth over time.

Plant roots are especially interesting because they can create unusual streaks or light-colored patterns on fossil shark teeth, particularly on the enamel. As roots grow through sediment, they release weak organic acids and change the chemistry of the surrounding soil. These chemical changes can slowly dissolve or leach minerals out of parts of the fossil tooth.

Because roots often grow in thin branching patterns, the mineral loss may occur only along narrow pathways where the root was touching or growing near the tooth. This can produce pale streaks, branching lines, or lightning-like patterns across the enamel surface. In some cases, the streaks follow tiny cracks in the tooth where water and root acids were able to penetrate more easily.

Collectors sometimes mistake these patterns for natural enamel color or feeding wear, but they are actually a type of post-fossilization chemical alteration caused by the surrounding environment.

How groundwater can change the color of shark teeth

Groundwater is one of the biggest reasons fossil shark teeth change color after fossilization.

As groundwater slowly moves through sediment, it can either add minerals to the tooth or remove them. In some cases, groundwater leaches minerals out of the fossil, causing the tooth to become lighter in color over time.

This process can affect only part of the tooth, creating different colors in the root and enamel. In extreme cases, the original dark fossil color may be almost completely removed, leaving the tooth white or cream colored again. Some heavily leached fossil shark teeth can even resemble modern shark teeth.

Other reasons fossil shark teeth can have streaks, spots, or unusual colors

There are many smaller factors that can produce unusual colors and patterns in fossil shark teeth.

Cracks in the sediment can channel mineral-rich water toward only certain parts of the tooth. Plant roots growing near the fossil may alter the chemistry of the surrounding sediment. Animal burrows can also change how oxygen and groundwater move through the deposit.

These localized changes can create streaks, spots, speckling, cloudiness, or even polka-dot patterns in fossil shark teeth.

As a result, no two fossil shark teeth fossilize in exactly the same way. The wide variety of colors and patterns seen in fossil shark teeth is a natural part of both the fossilization process and the environmental changes that happen afterward.

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Why Shark Teeth Are Different Colors in Different Locations (Real Examples from Famous Fossil Sites)

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Fossil Shark Teeth from Calvert Cliffs, Maryland

At the famous Calvert Cliffs in Maryland, many fossil-bearing layers consist of bluish and greenish clays mixed with brown sands and iron-rich sediments. Because of this combination of minerals, fossil shark teeth from Calvert Cliffs are often multicolored. It is very common to find teeth with a mix of blue, green, gray, and brown tones all in the same tooth.

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Fossil Shark Teeth from the Big Brook area of New Jersey

In New Jersey, many of the Cretaceous shark tooth formations are rich in iron oxide, which is essentially natural rust. This iron gives fossil shark teeth and other fossils from these layers their well-known red and orange colors. That is why shark teeth found in New Jersey are often bright red, reddish-brown, or deep orange.

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Fossil Shark Teeth from Venice Beach, Florida

The Peace River formation in Florida is extremely rich in phosphate, which is a dense black mineral. Because of this, fossil shark teeth from the Peace River are most commonly black. The Venice Beach collecting area and the Peace River collecting area are both well known for producing large numbers of black fossil shark teeth.

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Fossil Shark Teeth from Coastal South Carolina

The coastal rivers of South Carolina are known as blackwater rivers because they contain high levels of tannins from decaying plant material. These tannins give the water a dark brown color, and fossil shark teeth found in these rivers often absorb that color. As a result, shark teeth from South Carolina rivers are frequently dark brown or almost black.

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Fossil Shark Teeth from Aurora, North Carolina

Fossils from the Pungo River Formation at Aurora, North Carolina are preserved in sediments that contain a lot of phosphate. However, the surrounding limestones and other sediments are usually gray. Because of this combination, fossil shark teeth from Aurora often have a distinctive grayish-yellow or gray-tan color that is very different from the deep black teeth found in Florida.

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Conclusion: Why Fossil Shark Teeth Come in So Many Colors

Fossil shark tooth color is not determined by the age of the tooth or even the species of shark it came from. Instead, it is controlled almost entirely by the minerals in the sediment where the tooth was buried and fossilized. Iron-rich sediments can produce red, orange, or brown teeth, phosphate-rich environments often create black teeth, and other mineral conditions can produce shades of blue, green, gray, or even white.

Besides for sediment chemistry, diagenetic processes, meaning the physical and chemical changes that occur after burial during fossilization, also play a major role in determining final color. As diagenesis progresses, groundwater and dissolved minerals can alter the original composition of the tooth, sometimes changing colors unevenly within the same specimen. This is why a single fossil shark tooth may show a dark root, lighter enamel, or streaks and mottled patterns.

So why are most fossil shark teeth black? The simple answer is that phosphate is extremely common in many marine fossil deposits, and over time it replaces the original material in the tooth during fossilization and diagenesis. However, shark teeth can come in many different colors, and even shark teeth of the same species and age can look completely different depending on where they were found.

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Scientific Sources

Feichtinger, Iris, et al. (2020) Fossil microbial shark tooth decay documents in situ metabolism of enameloid proteins as nutrition source in deep water environments. Scientific Reports. doi:10.1038/s41598-020-77964-5

Dauphin, Yannicke. (2022) Vertebrate Taphonomy and Diagenesis: Implications of Structural and Compositional Alterations of Phosphate Biominerals. Minerals. doi:10.3390/min12020180

Kocsis, László, et al. (2023) Enigmatic carbonate isotope values in shark teeth: Evidence for environmental and dietary controls. Palaeogeography, Palaeoclimatology, Palaeoecology. doi:10.1016/j.palaeo.2023.111943

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