The coin and the pendant are silver based on my testing kit. Paid $90 for it in Europe. Thought it looked nice for a chain. The Jalapeno pepper on the reverse does challenge me a bit.
Real or not, it isn't Alexander. And that's a cornucopia on the reverse. Your picture isn't large enough for me to read the reverse legend. If its fully silver, its likely from the Cappadocian Kingdom. If its plated, its probably a Seleukid bronze coin.
Do I read Demetrios? http://www.acsearch.info/record.html?id=93913 If so, it could be silver and, if genuine, worth more than the price. That is a big 'if' since a cast copy would make a nice pendant as well and still sell for $90.
Interesting point. I find it especially hard to determine the genuineness of Ancients due in part to the fact that they not all struck equally and proportionately. I did test it and it is showing up as silver. Can the coin be a silver cast copy? And did I do poorly by paying $90 if it is? Expert opinions needed! :Bigger photos:
My opinion is that a coin mounted as jewelry is no longer a coin but, in this case, a necklace. I'd think a pretty silver necklace is not badly priced at $90 but I'd not wear it for fifty years and expect the coin to come out as good as it was when it went in. For that reason, I'd use a fake for the purpose if I wanted a necklace. I'd not buy a coin damaged by prong mounting for that much so it come back to whether you want a coin or a necklace. If being a real coin is important to you, the item needs to be shown to someone who knows the series in person. Based on the photo, I'd not buy the coin as genuine but I'm no expert in Hellenistic silver and preparation for mounting could include abuse of the surface that could make a good coin look fake. The style looks correct so the question is whether the coin was made from dies 2000+ years ago for from a jeweler's casting mold circa 2010.
Due to the softness in the recessed design, I would say that it is most likely a cast. I am somewhat happy thinking that a real coin was not used for a pendant.