Yes, a jack of diamonds can fit in even the tiniest of chimneys.
(A quick aside: One of my favorite holiday specials was Christmas on Sesame Street. The A-plot is Big Bird trying to figure out how Santa can fit down the tiny city chimneys on Christmas. Kermit interviews a bunch of kids and my favorite answer is “Santa sneaks into the house during Thanksgiving and hides in the laundry room until Christmas,”)
What goes great with ice cream?