Those look a lot like Blundell Buttons. They are quite valuable actually. They tend to be different colors in different lighting. Sometimes a lot of green mottling and even purple.
Officially they are Protopalythoa Grande, but were named Blundell Buttons ~14 years ago after the person that brought them to the attention of the hobby, around this locale anyway.

The reason I know this is because Adam gave me some of the first ones he collected.