Yep, it sure looks like Fatimid gold. The size and weight are compatible with a ruba'i or 1/4 dinar of the early period.
I have a hard enough time reading Kufic script on even the best-preserved specimens, and this coin is quite well worn. But the style of the lettering seems closest to that of Al-Mu'izz. Compare it with the quarter-dinars you can see on
the zeno.ru pages for this ruler.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis