It was a little confusing to see you say, "there appears to be no pontil," since obviously the marble has a pointil. I take it you mean that you're not seeing the roughness you might expect on one of the ends.
I don't have much technical knowledge about handmades so I'm just moving this to the main chat forum and hope someone else will help out with observations.
In the meantime, it might be helpful if you added an photo of the whole marble.
Thanks!