Well it does not look like it was a piece of something larger. I'll stay with it probably being art glass. Still will sell and get you a few gallons of gas. Nice find. Thanks for the extended pics. Cool looking.
Those photos illustrate why one should almost always include something to provide scale in their pictures when seeking information on their finds, especially when trying to identify mystery items.
The first photos had me thinking paperweight like another member suggested. Now that I see the item is merely fingertip-size, I can't imagine it would make an effective paperweight.
The "base" doesn't look like it was ever attached to, or broken off, a larger structure. I'm inclined to think it is just a random bit of decorative glass*; or perhaps a partially melted marble?
What is the age and context of the dumpsite? Was the dump burned?
*In my late mother's house, I found a bowl full of gobbets of glass of various colors, shapes and sizes (all smaller than 1-1/2" length). They are not beach glass, as all are glossy smooth. Although my mother did not keep pet fish, I think such glass is sometimes used for aquarium decoration in lieu of a sand bottom.