Potential Fossil Shell I’ve Wondered About For Years

[NerdMaster9000]

Years ago, (More than 10 now) on a venture to Dauphin Island, AL I came across a deposits of shells, two of which were very surprising to me when I first picked them up. 
 

These particular shells were not surface level, but rather slightly buried under a few (~3)inches of beach deposit. 

When I fully brushed the sand away and got a full view of them, I assumed because of their shape and color they were particularly large modern shells.

 

However as soon as I touched them I realized their weight and density were not that of shell, but much more akin to rock.

 

I’ve asked as many people as I’ve been able to show them to, no one seems to have any understanding (or interest for that matter) in the question. 
 

Do these specimens seem like they could possibly be petrified or fossilized? From my purely amateur and ignorant observations, it feels likely. 
 

I’d absolutely love to hear anyone’s thoughts and opinions on this! It’s something I’ve been very curious about for years, and I very much appreciate any informed discussion!!
 

[Fossildude19]

@MikeR   @Coco 

[Thomas.Dodson]

They look more modern/sub-modern to me but that doesn't mean they aren't fossilized, some pleistocene and pliocene fossil shells look like this. As for what they are, they look like a Mercenaria. It is worth noting that Mercenaria have thick and dense shells which could seem more rock like. Could you tell us more about this beach deposit? Was it sand/mud/etc.?

[NerdMaster9000]

@Thomas.Dodson Thank you so much!

I am now going to look into Mercenaria to widen my understanding.

 

As for the environment the deposit was in, I’d say it was mostly beach sand/alluvial sediment substrate consistent with the Mississippi River Delta area. This was also in a more grassy area, for what it is worth. I’d imagine that particular area experiences less wind erosion because of the grass/roots. 

[Coco]

Hi,

 

Despite its erosion due to the sea, the fact that it is not whole and traces of predation (small holes) it seems to me, I think it is a current shell.

If it’s not a Mercenaria, it’s certainly a shell of the same family.

 

Coco

[minnbuckeye]

Dauphin Island seems to have had a recent beach replenishment project that exposed many fossils from the Pliocene. Hence, I am in support of this being a likely fossil Mercenaria.