The finest blue moonstone in the world comes from a small area of southern Sri Lanka around Meetiyagoda, where miners sink narrow hand-dug pits into the clay and haul the gravel up in baskets, much as they have for generations. The blue sheen (adularescence) of Ceylon moonstone is the standard for the gem. PUBLIC mine visits are common in the area; buy in Ambalangoda or Ratnapura.
Moonstone
See it on the map
Other places on the map within a couple of hours.