How much is a 1916 silver dime worth?

I have a coin that looks like the picture of a Mercury dime, it's 1916D.
But it is about the size of a Baseball. Is it even real?

No - it's a novelty item that sells for a few dollars in gift shops. There are several companies that make coasters and paperweights, usually about 10 cm in diameter, that carry the date and denomination of famous US Coins.