This colorless oval could have possibly been heat treated since it went threw Thailand from where ever it was mined. The principle reason I purchased the rough was to see if heating effect it, in a way that I could tell. I wasn’t able to see any difference in the four pieces I bought, from run of the mill unheated tourmaline.
This oval is eye clean and completely colorless. It weighs 3.16 carats. I have some identically colorless tourmaline that I feel sure was not heated. The inability to determine heating or not, makes the heating question of little consequence.