I second this recommendation! The museum alone is worth the trip, but it's also close to copper harbor and lots of rock hounding opportunities. I want to go back for more copper inclusion agates.

It can occur naturally, and I would assume this is a natural one because it was in an excellent museum where they probably would have mentioned if it was altered.

Basically, when it’s found, it’s usually yellow, but as the copper and iron in the mineral react with oxygen and moisture over time, it develops a thin iridescent tarnish.