1971 D Kennedy - What causes this feature?

[AMG]

What causes this, for lack of a better term, 'halo effect' around the lower half of Kennedy's bust? I see this same feature on some of the Kennedys on PGCS. The whole texture of the coin is grainy, but that grain is minimized in the halo, thus reflecting the light differently. I assume something in the process of striking the coin causes this, but the feature isn't evident on all the coins I looked at. I rather like this coin, it's fairly pristine looking. Thanks in advance for the education.

[SensibleSal66]

What kind of holder is it in ?

[SensibleSal66]

I'm not an expert but maybe it is Oxidation ( if that's possible on Clad) OR "toning " . Not gonna hurt value.

[Daniel]

It's die deterioration. You're see the metal flow lines from a die that is breaking down.

[AMG]

Ah, thank you Daniel. Sal, it's just in a cardboard flip.

[Paul]

The "Halo Effect" that you are seeing, is the result of die polishing....
Notice the radial striations in the fields ...... as they are indicators of a late die state strike.