Help identifying mystery rock?

[ArtnSoul]

Hi all, I'm new here and I was wondering if anyone knows what kind of rock this is? My Dad found it over 50 years ago in the edge of the Northeast River in Maryland. It rattles/knocks inside when shaken and it is very heavy relative to its size. Any help is greatly appreciated

 

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[ArtnSoul]

The coin next to it in the last pic is a quarter