Not sure what this could be but I saw one similar to this but online. Put it in a holder before taking a good pic of it sorry if it’s hard to see.
I believe, from my experience (which isn't a lot), that is a cud. Not a very large one, but still cool.
Need photo of obverse to verify Cud. Cuds are caused by a broken or chipped die which results in no design features on opposite side. http://www.error-ref.com/cuds/ It looks more like a lamination issue. Cuds are usually raised above the surface of coin.
