This Christensen Agate "guinea" marble, the largest example known to exist, sold recently for US $2,627.99.
At one inch in diameter, this marble came from a group of three that were almost certainly prototypes of the Christensen Agate guinea marble style that today is one of the most collectible.
I think its new owner should take this spectacular treasure on tour to all the marble shows and charge collectors just $10 to hold it for one minute (in a padded room of course, with everyone wearing gloves).
I'd be first in line.
Picture courtesy of Alan's Marble Connection store.