Ouch. I have never seen a bronze coin do that but the photo shows that it had
very unusual internal corrosion. Clearly not your fault.
I've smashed a few coins in my time. More often crystallised silver. MY Republican
bronzes seem to be immune to bronze disease
, possibly because of the high lead content (not sure what that does). Or it may be that I rarely buy cleaned bronzes (prefer a little residual crustiness), and I NEVER clean my coins. Someone on this list remarked a while back that rampant bronze disease
almost always has to relate to human intervention (because logically speaking, if the coin had
such a big problem when in the ground 2000 years ago it would have disintegrated 1995 years ago).
One time I bought an evidently fragile but entire crystallised silver coin and received a small bag of dusty fragments. I didn't complain - I got what I knew I was buying