Hi,
As Raphael has provided a picture - that is what your "slug" once looked like. You have the Metal(Brass) Core of the Casino Chip. The Plastic/Composite part of the chip has been melted off or removed somehow. A complete $25 Chip as shown in Raphael's scan goes for about $40-$60 on EBAY right now. In My opinion what you have is probably worth about $5 or so just as a novelty, but others may disagree with me. I have seen examples of these chips where someone has taken the core and re-molded it - both in the correct color and also incorrect colors(Blue, Pink & others). If you found someone who wanted it for such a unique purpose you might get more for it, but I still doubt it. Hope that helps.
Peace,
Don