Many years ago, I found a piece of rock on a lakeside in Switzerland (see picture below). I think that it could be a "fossil" from some Pecten species (do you agree?).
My question is: how old such a fossil can be, approximately? Is it like 1000 years, or rather 1'000'000 years?
I have no idea, that's why I just would be interested to have your opinion on this topic. I don't know if it is frequent or rather uncommon to find such "fossils".
Thank you for your help!