I have written about the bluestone pebble found in Durrington which is fully reported in "Along Prehistoric Lines: Neolithic, Iron Age and Romano-British Activity in the Former MOD Headquarters, Durrington, Wiltshire" By Steve Thompson and Andrew B. Powell Published by Wessex Archaeology, 2018 and summarised at https://www.wessexarch.co.uk/our-work/mod-durrington .
"A discoidal 'bluestone' object with heavily ground and flattened edges was found in the tertiary fill of the northern terminal of Romano British ditch 6256 (slot 5145), 7 m from the intersection of the two Late Neolithic posthole alignments (at posthole 5047). The object, which has a rounded trapezoid shape, is 64 mm wide, 67 mm long and 18 mm thick. It is made from a slab of stone that has developed a light grey surface patina, although a fresh break in one corner suggests a poorly developed conchoidal fracture and is a dark grey colour when freshly worked."
Pessoi are rarely mentioned as a use for lithics and ceramics though before the luxury of Andrex they were commonly used. Elsewhere pessoi discs are described as 3-10.5 cm in diameter and 0.6-2.2 cm thick. Pessoi, Greek for pebble, is the correct term for lithic ones but is often used for pottery ones, which are also called Ostraka (Ostrakon sing.), which were "re-cut from old broken ceramics to give smooth angles that would minimise anal trauma". Ostraka have the added bonus that you could scratch the name of a person you wanted to Ostracize on them.
The Durrington Bluestone is exactly the right shape, size and context to be one, I wonder whether this posh souvenir from Stonehenge was one?
As an update as I was walking the dogs on the path where occasionally I find a bit of Roman pottery I noticed with fresh eyes a flint disc. I have seen something similar before, it has a crudely worked edge which is smooth rather than either a cutting edge or a bashing edge as most flint tools are.