The material is in doubt. I think it might be glass or even faience. If it is in the quartz family it's more likely to be quartz than agate. And, if it is quartz it is very possible the bead was glazed. Glaze being glass, the bead would then have a glassy aspect—that I think I can see in your photo. Plus, there are places where it appears parts may be absent. This could happen to the bead, whether it is quartz, faience, or glass.

Can you say how the bead was determined to be agate?

Jamey

I have hundreds of these and have drilled and cut and ground many. They are agate , they are layered as agates are layered. What makes them unique in form is that they formed in ore deposits by secondary solutions infused with quartz , a very common phenomena but rare in ore deposits. Many are sagenitic and very textured and a fair amount of them have black copper oxides on the surface or incorporated in voids. When cutting them the green swarf coming off the stone indicates copper. The carnelians are very interesting as well as a few are cherry red and quite saturated.