Do you remember the iconic poster for the movie Jaws?
The one where the shark is coming up from the depths with its open mouth filled with rows of razor-sharp white teeth.
Well, stereotyping aside, the tooth color is accurate. Living sharks have white or cream-colored teeth.
So, why are shark’s teeth black when you find them?
Like modern sharks, ancient sharks frequently dropped teeth while going about their everyday lives.
Surrounding minerals, particularly phosphate, in the sediment the dropped shark tooth was buried in were slowly absorbed in a process called permineralization.
This caused the tooth to become black as fossilization preserved it.
We’re going to look at exactly how this happens and also find out how you can find shark teeth in several other colors.
Why Are Sharks Teeth Found on the Beach Black?
A living shark has a normal whitish tooth color, the same as a healthy human.
Why are shark teeth found on the beach black? Fossilized teeth have changed color because when a shark tooth is preserved, it takes on the minerals from the sediment around it and eventually changes color – often to black.
A black shark tooth is a fossil that could be hundreds of thousands or even millions of years old.
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The long preservation process that petrified shark’s teeth go through began when the prehistoric shark dropped them.
Just like modern sharks, ancient sharks could lose as many as 40,000 teeth during their lives. Sharks have been around for about 420 million years, so you can imagine through the millennia, there have been a lot of dropped shark teeth to turn into fossils.
To get preserved, the shark tooth had to fall into the right kind of sediment.
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The sediment needed to quickly bury and protect the tooth from oxygen and bacteria that would otherwise decay it on the ocean floor.
As it prevents decomposition, layers of sediment built up above the buried tooth, and pressure increased, pushing minerals from the surroundings into the shark tooth in a process called permineralization.
Minerals took the place of the organic material inside the tooth, and slowly but surely, as the minerals crystallized within the pores, the shark tooth was preserved as a fossil.
So, why do sharks’ teeth turn black? The black color comes from the phosphate-rich sediment that a tooth ended up getting buried in.
For example, phosphate is a dense black material, so when a tooth was fossilized, it took on this dark color.
Black shark teeth are particularly well-known amongst fossil hunters in Florida as the geological layers are rich in phosphate.
How Long Does It Take for Shark’s Teeth To Turn Black?
So, we’ve answered” why are shark’s teeth black” by discovering that it’s down to the type of mineral-rich sediment they were fossilized within.
Now, it’s interesting to consider how old are fossil shark teeth.
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It takes a minimum of 10,000 years for a shark tooth to fossilize. However, the shark teeth you’re likely to find are probably much older.
Paleontologists can analyze how old preserved shark teeth are by studying the age of the sediments in which they found the teeth using geological maps.
That’s fine if you find shark teeth buried in the prehistoric sedimentary rock. However, if you find a shark tooth on its own in a river or at the beach, it can be trickier to age accurately without complex chemical analysis.
Another good indicator of age is identifying the shark species the tooth came from. If that’s possible, you can look up when that shark lived to narrow down the age of the tooth.
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Most of the shark teeth found are from between the Upper Cretaceous (100.5 million years ago – 66 million years ago) and Tertiary periods (65 million years ago – 2.588 million years ago).
The area in Florida, known as Bone Valley, produces black shark teeth thanks to its phosphate-rich geology. Most shark teeth found here are between 3 and 10 million years old.
So, if you find a black shark’s tooth, it’s likely to be at least a few million years old!
What Color Are Sharks Teeth Besides Black?
Are shark’s teeth always black? No, fossilized shark teeth can be found in many other colors, including blue, green, brown, and even patterned.
The shark’s teeth’ color depends mainly on the mineral content of the sediment they were preserved in.
You’ll unlikely find a white shark’s tooth unless you’re really lucky. A freshly dropped shark’s tooth is unlikely to wash up on the beach, although it is possible.
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You’d need excellent eyesight to spot modern shark teeth amongst the similar colored sand and shell fragments.
If a shark’s tooth doesn’t get buried and eventually fossilized, it will be broken down and disintegrate.
What Factors Can Affect the Color of Fossilized Shark Teeth?
Although it can sometimes give an idea, color isn’t a good indication of the approximate age of a shark tooth. This is because many factors can determine the final color that fossilized shark teeth have.
The Chemical Composition of the Sediment
As we’ve already mentioned, black shark teeth get their color from being preserved in phosphate-rich sediment.
Iron-rich sediment can produce red, orange, or brown fossil shark teeth, while clay and limestone-rich substrates can make the colored teeth grayish green to graying yellow.
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Mixed chemical composition sediments can result in shark teeth fossils with a mix of colors and even spots or brown, blue, and green stripes.
pH of the Sediment
How acidic or alkaline the sediment and water were when the shark teeth were fossilized can affect the color.
The chemistry changes how quickly certain organic parts of the shark tooth are destroyed, which can adjust how densely the sediment minerals crystalize in the tooth.
Exposure to Groundwater
Once the shark tooth fossil is formed, if it’s kept dry, the color will probably stay the same until it’s discovered.
However, if freshwater runs through the ground, the minerals inside the shark teeth can get washed out somewhat, causing them to become lighter.
Fossilized shark teeth often turn a deeper color of dark brown in areas where the groundwater contains tannins, such as in South Carolina.
Are Black Shark Teeth Rare?
Black shark teeth are not especially rare as the phosphate mineral that gives them their color is reasonably common.
However, what is rare is well-preserved black fossil teeth.
Shark teeth found in creeks and rivers will probably have been tumbled about and worn away by the movement as they’ve been removed from their sediment home by the water.
Similarly, shark teeth found at the beach will probably have been worn by crashing waves.
The rarest and, accordingly, the most valuable shark teeth are the ones in the best condition. These will usually be teeth found still inside the rock that they were fossilized within.
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Bigger shark teeth can also be highly prized. For example, a well-preserved megalodon tooth can sell for thousands of dollars.
Conclusion
Fossilized shark teeth can be found in many colors, and one of the most commonly found is black.
Why are shark’s teeth black? It’s because they’ve been fossilized inside sediment with high concentrations of phosphate, which is black in color.
The fossilization process takes a minimum of tens of thousands of years, and during this time, the buried shark teeth take on the minerals surrounding them.
If you’re lucky enough to find fossilized shark teeth at the beach or in a river, the color that they are can let you know how they were preserved.
As well as black shark teeth, you may find fossilized teeth with orange, brown, green, dark gray, yellow, or even striped or spotted colors.
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While there are other reasons, the main factor that gives a preserved shark tooth its color is the composition of the common minerals in the sediment that it fell into millions of years ago.
British-born Dan has been a scuba instructor and guide in Egypt's Red Sea since 2010.
Dan loves inspiring safe, fun, and environmentally responsible diving and particularly enjoys the opportunity to dive with sharks or investigate local shipwrecks.
When not spending time underwater, Dan can usually be found biking and hiking in Sharm's desert surroundings.
That was very informative. Thank you.