Can anyone tell me what caused this - Proof 1970 Quarter

[jgrinz]

Is this a Lamination error - Looks like you can see to the core of the coin

 

 

[cladking]

There should be a sharp ridge around the hole if it's really a hole in the cladding material. This would be most unusual so I'd suspect it's something struck in instead. Copper flecks and pieces aren't extremely uncommon like this.

[errorist]

I'd say a strike thru error also.