Hello. Welcome to the forum.
At well over an inch in diameter, that is almost certainly a foreign marble. Probably a Vacor, from Mexico.
The current company making them is Fabricas Selectas, if I'm up to date. We call them Vacor because it's so much easier, and because that was once the company's name.
It's a modern marble, likely made after the year 2000.
You could set the price for a few dollars and see what would happen. Such a large marble might sell for more than the average Vacor would.