Excellent question derkerlegand. It weighs 2.99 g, so it is a little lite. In looking at it more closely the last number in the date looks like an 8 and the 9 looks very thick and higher that it should be. These two numbers are VERY hard to see however.
A thin planchet should show weakness on both sides. I think it looks like a struck though debris / grease.
The low weight, granular texture, and absence of the obverse design rim on the right strongly suggests that the design was mechanically removed outside the Mint, possibly by sand-blasting or a similar technique. The granular texture also appears on the reverse.
As an alternate possibility, I think it was exposed to acid myself, but only because it is easier to throw it is a strong lab acid than hold it and sand blast with the high pressure. But Mike probably got it !! Maybe a diameter measurement would also help . Jim