This is actually part of a large scale 'gag' perpetrated by a few of my friends in the prop community. In 2002 or so, I coined the phrase "Z-list prop", which refers to a prop that is ultra lame, undesirable, and adds nothing to a collection.
This term came about from a radio interview I heard, in which the host referred to his line up for the afternoon as "A bunch of Z-List actors". The term comes from the hollywood biz, were actors are placed on the "A list", "B List" or "C List". "A list" actors would include people like Tom Cruise, Arnold, Tom Hanks, Charlize Theron etc. People who are very bankable and tend to be in high profile movies. "B List" actors are the next rung down and so on. So, I figured we could apply this terminology to the prop collecting game. A list props are things like hero lightsabers that were used in the films and stuff like that. At the very ass end of the collecting game are the Z-list props. These are the props that are so lame, saw so little time on screen, are so uninteresting, or have so little to do with the plot that it boggles the mine.
Don't get me wrong. I've got my fair share of z-listers in my collection. And boy, do I regret it!
Anyhow, this is a glass marble. Nothing more. Was it what they used in the movie? Who knows. More importantly, who cares.