This is why I posted in the crazy ideas thread!

I don't know how they could have made the bigger stones represented by tokens. Nevertheless, the stones didn't have to be divisible or transferable to be used as store of value and trade.

The places where there happen to be thousands of stones aligned in the same place, like Carnac, could have been big annual markets where they traded goods, lands, political agreements, slaves, wives, etc.

https://en.wikipedia.org/wiki/Carnac_stones