Forum:Found a black chest underground that won't open?

Was digging underground and I noticed that there was a light source east of where I currently dug myself. I looked closer and it was a charcoal colored chest underwater with what looked like horns coming out of it. I immediately went over and dug in such a way that the water would drain and i could access the chest. There were also black colored sparkles shooting out in all directions from the chest in a small radius. When I got there, right clicking and left clicking did nothing. The only interaction I could have with the chest was if I pulled out my wooden hammer and tried to bust it open. This didn't work.

Every time I swung the hammer I would take damage, but the chest would not open. I tried digging the ground directly beneath it, but it won't even allow me. I was able to dig 2 tiles underneath it, so the chest is now floating on 3 tiles of dirt in the air, but I can't interact with it.

I've tried googling endlessly and going through every item on this wikia page hoping I will see a picture of some kind of post about this object, but there's nothing. I have no idea what it's called or what I'm supposed to do with it. Any help is appreciated.

I don't have a screenshot on me, but I can upload one tonight or this weekend in hopes that someone will recognize whatever the hell I found and what I'm supposed to do with it.