Any ideas?

[deepseabob]

I found this rock(?) about thirty years ago on the bottom of Long Island Sound in about 50 feet of water just outside the entrance to the Thames river in Groton CT. It was just sitting on the bottom with nothing else around it but white sand. I've always been curious of what it could be, any ideas?

 

[rock]

Looks like a big piece of Chert or Flint which ever you prefer to call it. It has some nice river patina on it show it has been underwater for a long time. Welcome to the site, rock

 

[Eu_citzen]

A daylight picture would be useful. Also do a streak test - rub it against an unglazed piece of porcelain. What colour do you get?