Shark Tooth? Any information?

While I was cleaning my crystal collection (achieved by dumping the whole lot in the bath!) a few weeks ago I found this tooth. I gave it to my best friend's son, who I regard my nephew, as he collects shark teeth. I am still curious to obtain more information on it if anyone knows anything. If not, it is still a very cool picture! 

My friend is (jokingly) mad at me, as I was the one who began her son's obsession with shark's teeth by giving him a necklace wit a shark's tooth a few months ago. Since then he has changed the whole theme of his bedroom to "sharks", with bedding, curtains and decor to match!

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