Is This A Delamination Error?

Upon further inspection. That dark spot on the reverse has me suspicious it was heated. that may have created the issue.

Looks like a clam shell or a split planchet. I can't find the exact term for this one on Mike Diamond's web site. Looks like a legit error to me.

This is called a Hinged Split Planchet or "Clam Shell Lamination". I once had one on a 1969-S Proof half dollar that I put up for auction and went for less than $100. I was bummed!

The deffinition can be found on the The CONECA
Glossary of Error-Variety Terms (http://conecaonline.org/content/glossary.html) as:

"These planchets have not fully split apart but remain connected by a small piece of metal, or "hinge." They are often referred to as "clamshells.""

Here is a nice one on a 1939 Jefferson nickel.