No idea of construction materials or manufacturer. If clay, likely made by Burt Co. If plastic, who knows.
@David Spragg or somebody on thechipboard would be a better source for info.
EDIT: Update
Turns out they are clay compression-molded chips, manufactured by either
USPC (pre-1947) or Burt Co (Maine) and distributed by Ryan & Co. ("S" mold chips were later sold by both HE Mason & Co. and Taylor & Co. after Ryan & Co was sold).
No clue what they are worth, but undoubtedly worth more than $24 to somebody in the collecting world. I would not break up the set.