It's split plate doubling. The pressure of the strike broke the copper plating and exposed the zinc core. While it's interesting and is very impressive, it's considered damage and reduces the coins value. I don't know of anyone that collects split plate doubled coins.
I'm interested in the small anomaly on the reverse rim at K:5. Tiny clip? Anyone know what it could be?
The first US coin motto was found on a 1792 half disme and read: "LIB (erty) PAR (ent) OF SCIENCE & INDUSTRY"