Mica Swirls frequently have "ghost" and/or "filament" cores. A ghost core is a bunch of little air bubbles all contained within an ethereal "sheath. The "Moonie" is most often affiliated with machine designed marbles, significantly Akro Agate and Christensen Agate. On the other hand, some hand created examples do exist. http://caidengwlan.timeblog.net/12611355/the-single-best-strategy-to-use-for-marble-watches