If you’ve ever found a shark tooth on a beach, along a riverbank or in a fossil deposit, you may have wondered why it’s black instead of white.
After all, the teeth in a living shark are generally white or cream-colored. So why are fossil shark teeth often black, brown, gray—or sometimes even blue, red or orange?
The answer is one of the most interesting parts of fossilization.
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The color of a fossil shark tooth usually comes from the minerals and sediments surrounding the tooth as it fossilized.
In other words, that black shark tooth wasn’t black when it was inside the shark. Its color is part of the geological story of what happened to it after it was lost millions of years ago.
How Does a Shark Tooth Become a Fossil?
Sharks continuously shed and replace their teeth throughout their lives. A single shark can lose thousands of teeth, which helps explain why shark teeth are among the most commonly discovered shark fossils.
When a tooth falls to the seafloor, most simply break down over time. But occasionally a tooth is quickly buried beneath mud, sand or other sediment.
Under the right conditions, groundwater slowly moves through those sediments carrying dissolved minerals.
Over thousands or millions of years, minerals can enter microscopic spaces within the tooth and alter its chemical composition through a process known as permineralization.
The tooth retains its original shape and structure, but it becomes increasingly mineralized.
Those minerals can also change its color.
That is why two fossil shark teeth from the same species can look completely different depending on where they were fossilized.
Why Are So Many Fossil Shark Teeth Black?
Black is probably the color most people associate with fossil shark teeth.
Many fossil-bearing marine deposits contain phosphate and other minerals and compounds capable of producing dark coloration during fossilization. Teeth preserved in these environments can become dark gray or nearly jet black.
This is especially common in fossil-rich areas along the southeastern United States.
The important thing to remember is that black does not automatically mean older.
A black tooth isn't necessarily older than a brown, gray or tan tooth. It may simply have fossilized under different geological conditions.
Why Are Some Fossil Shark Teeth Brown?
Brown, reddish-brown and orange fossil shark teeth are often associated with iron-rich sediments.
Think about what happens when iron is exposed to oxygen and moisture: it rusts.
Similar oxidation processes involving iron-bearing minerals can occur in fossil deposits. As those minerals interact with a buried tooth, they can produce beautiful shades ranging from light tan and brown to deep red and orange.
Sometimes these colors can be remarkably vivid.
And once again, they tell us more about the environment surrounding the tooth than they do about the shark itself.
Why Are Some Shark Teeth Gray?
Gray and blue-gray shark teeth can result from the particular combination of minerals, clays and other sediments surrounding the fossil.
Some fossil deposits are especially well known for producing gray, blue-gray, tan or even greenish teeth.
This is one reason collectors often become familiar with the appearance of fossils from particular locations. Over time, certain fossil deposits can develop recognizable combinations of colors and preservation.
However, color by itself usually isn't enough to determine exactly where a tooth came from.
Can Fossil Shark Teeth Be Other Colors?
Absolutely.
One of the fascinating things about collecting fossil shark teeth is the incredible range of natural colors you can encounter.
Depending on the fossilization environment, shark teeth may be:
- Black
- Dark gray
- Blue-gray
- Brown
- Tan
- Cream
- Red
- Orange
- Greenish
- Bluish
Some specimens even contain several colors in the same tooth.
You might find a tooth with a dark root and a lighter crown, or one containing streaks, patches and subtle variations in color.
These aren't necessarily imperfections. For many collectors, unusual natural coloration can make a fossil especially interesting.
Why Can the Root and Crown Be Different Colors?
Take a close look at a fossil shark tooth and you may notice that the root and crown aren't exactly the same color.
There's a reason for that.
The different parts of a shark tooth don't have exactly the same structure. The hard outer portion of the crown is extremely mineral-rich and resistant to alteration, while other portions of the tooth are more porous.
That means minerals can affect different parts of the tooth differently during fossilization.
The result can be a dark root with a lighter crown—or other contrasting patterns that give an individual fossil its unique appearance.
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Does the Color Tell You How Old a Shark Tooth Is?
This is one of the biggest misconceptions about fossil shark teeth.
No. You generally cannot determine the age of a fossil shark tooth from its color alone.
A jet-black tooth isn't automatically millions of years older than a gray or brown tooth.
Color is primarily a reflection of the geological environment in which the tooth fossilized.
To estimate the age of a fossil shark tooth, you need information about where it was discovered and the age of the geological formation or sediment layer that produced it.
For example, a fossil identified as a megalodon tooth must come from rocks or sediments dating to the time when megalodon existed.
Color alone can't tell you that.
Does Color Tell You What Species of Shark It Came From?
No.
A black tooth isn't a particular species, nor is a gray or brown tooth.
Shark tooth identification is based much more heavily on characteristics such as:
- Overall shape
- Crown width and length
- Serrations
- Root shape
- Cusplets
- Cutting edges
- Tooth position within the jaw
That's why two teeth belonging to the same species can be completely different colors.
One may be black while another is gray, tan or brown simply because they fossilized in different places.
What About Bone Valley Shark Teeth?
Florida's Bone Valley region is particularly interesting to fossil collectors because teeth from the area can exhibit an impressive variety of colors.
Rather than only the classic black associated with fossil shark teeth, Bone Valley specimens can occur in shades of gray, blue, cream, tan, brown, orange and combinations of several colors.
This natural coloration is one reason certain Bone Valley shark teeth are especially attractive to collectors.
Two teeth from the same species can look dramatically different, making every specimen unique.
Are White Shark Teeth Fossils?
Sometimes—but color alone isn't enough to determine whether a tooth is fossilized.
A recently shed shark tooth will generally be white or cream-colored, but fossil shark teeth can occasionally remain relatively light or become lighter because of the particular chemistry and geological processes they experienced.
That's why identification should never be based on color alone.
Where the tooth was found, its weight, texture, preservation and geological context can all provide additional clues.
Every Fossil Shark Tooth Has a Geological Story
That's one of our favorite things about fossils.
A fossil shark tooth doesn't just tell us about the animal that once carried it.
It also records part of the environment in which it spent thousands or millions of years buried underground.
Its shape can help tell us what kind of shark it came from.
Its geological location can help tell us when that shark lived.
And its color can provide clues about what happened to the tooth after the shark lost it.
So the next time you're holding a black, brown or gray fossil shark tooth, take another look at the color.
You're not simply looking at an old tooth.
You're looking at millions of years of geology written into a fossil.
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