Quarter composition question

[Twitch]

This week I hunted a bag of quarters and found a lone '64-D, a 2002-S Indiana clad proof and a 1999-P New Jersey quarter with absolutely no copper showing on the rim. It weighs 5.7g so that's right for the quarter. It's definitely not silver so let's rule that out. This obvious answer is that it's plated but it doesn't at all look plated in hand or under the microscope. What are my other options? Any thoughts are appreciated. Pics below.

 

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[enamel7]

Sometimes the layers just happen to overlap that way. I see them on occasion.

 

[Liu21]

I bet there is someone out there that will pay more than face value for that uncommon error... lol