Alexander III coin

I've came across a strange coin. It was part of an deceased estate. The owner was an serious ancient coin collector in South Africa. Most of his coins was high value and of Roman origin accept for this one. Don't have much more information on the history. The coin is silver, 24mm and weighs 10.91 grams. (the weight makes it strange to me) further the back image is minted upside down.

Nice coin.is a tetradrachm from alex the great or phillip I ot II.try to search in numista cataloge under greece ancient-kings of macedon.

Exist a lot of different coins with different mintmarks.

Good luck

Thanks for the info, I really do appreciate the feedback. After closer inspection it was point out to me that it might be a fourrée. Because of the weight and if you look closely at the top edge you can see the copper core showing. The thing that boggles my mind is that the deceased owner was a serious coin collector. All his coins was cataloged with past purchased history , price paid ect. except  for this coin. It only shows the price he paid for it. 4000eur. no history , where he bought it from nothing. What am I missing here? This doesn't seem like a 4000eur coin.

The mint mark looks like a Corinthian helmet, so maybe Masembria?