It's definitely not a Jatim (wrong structure).

I think it's almost certainly an authentic and very nice late Byzantine or Islamic bead. However, I'm just a little doubtful because of the air bubbles in your close-ups. Not the presence of bubbles themselves - most ancient glass has a lot of bubbles, both internal and in the surface - but the consistency of the bubbles in the white glass reminds me of the artificial surface treatments in some of the recent fakes made in Java (see the first attached pic). But, of course, that sugar comb effect (it reminds me all too temptingly of the candy I was addicted to as a child in the UK!) is seen quite frequently in ancient beads, including Jatims (this little bead that was found in the Philippines, for instance), so I think you should overlook these lingering doubts. Yankee would know for sure.

Best,

Will