Did you read the ChatGPT link? I too thought you were nuts, but apparently some form of charcoal has been used as a filler material in rubber formulas in the early days of rubber.Say what you want.
But a very reputable table mechanic that worked for Orner Billiards in Indianapolis years ago told me they were made out of Charcoal.
I could even give you his name. Unlike that idiot u12armresl who keeps talking about people but won't give anybody any names.