That's like some kind of mother nature rainbow coin. Or better know as the environmental damage coin.
Is that what caused the arch-like indentation that is under the design. It doesn't interfere with the design.
It was most likely caused by another quarter resting on top of it undisturbed as it toned. Perhaps transferring over from that coin.
It would take pressure to make the indentation wouldn't it? Could it have been on the planchet before it was struck? Maybe a defective planchet.
It's beautiful but it was probably caused by something being spilled on the coin after it left the Mint.
