A friend of mine found this recently in the area of Belton, Texas in the undivided early Cretaceous.
He sent me the pic and asked if I knew what kind of crystal it was. I didn’t know so I asked him if I could post it here for him.
I’m not so curious about the fossil clam as the type of crystal it is.
If you need more pics it may take a while, because I think he is out of town for a while.
@ynot
It does not look like calcite really, but I suppose it could be. It just looks harder than that. I forgot to ask him to do a hardness scratch test. Let me know if you have any ideas.
Kim