This is a really cool find to show up in a second hand rock collectin. This was a donated piece and will earn change in the charity jar when it sells.

They do find marcasite nodules on the Jurassic coast in England so if I had to guess, I would put that as the most likely origin.

This piece of marcasite has lovely silvery insides with a brown bubbly looking outer shell. It's nice material but it is a soft-ish Mineral which is prone to crumbling. For that reason this is a display piece rather than a healing crystal.