This stone is listed as Canmore ID 63668 (go to Links).
It is a moss covered stone with a large worn ring mark and several cup marks visible in its current state. Canmore lists more ring marks but I didn't remove the moss to look for them.
Access to the site is by climbing up the slope of Cairnharrow for about 0.5 mile across rough ground or by a longer detour from Cambret Hill.