This is an Alexander III Silver Drachm (336-323). I recently purchased it and have…

It doesn't look entirely authentic but Incant rule it out from the photo. It's either not real or it's heavily worn with environmental damage and past cleaning. I would test the silver with an analytic probe if I had it in hand. You could pay to  certify it but it's not worth the price. You could also check the mass against similar coins in public auction records. My recommendation to you is to not get too hung up on this particular piece. Rather, try to attend Coin shows, perhaps take a course or join the ANA. it's a great way to learn about coins and acquire a collection.