I was not very familiar with this type at first glance, though I have seen similar examples. In Maud Spaer's "Ancient Glass in the Israel Museum", there is a very similar example, very close in shape to your friends. She refers to the one in the museum catalog as a "Demonic Mask Pendant", possibly from the Eastern mediterranean, circa 6th to 5th century BC.

I hope that this helps.

Jan Skipper
mosquitobay