It looks like an ancient agate bead, but the orientation of the hole and the fact it is only on one side is throwing me off. I have had, and handled many like it.
Sorry. I think I see the hole goes through and you are showing the top of the end in that picture.
Some of those agate beads cost a pretty penny.
Yours looks almost like the ones I remember as a "coca cola" bead. I may have the name wrong, but look at this site and see if you can find any like it.