It could be a result of the mixture of the alloy that , like some earlier Lincoln's ended up with a woodgrain effect. It would be better to see a picture of the obverse and the reverse of the coin, further back so that the entire coin could be seen. Thanks, Bill
It appears to be an issue with the alloy so i would call it a "woodgrain" effect at this point but I wouldn't rule out the possible influence of a chemical being used to create this effect. That being said, I lean toward the"woodgrain" concept. Thanks, Bill
I see no reason to suspect that is not natural. If you want to see some more, go to my home page and my album "woodies".