I would assume more is stabilized than natural, but I don’t know what the ratio is. Turquoise is a 3-6 on the mohs scale,
" Low quality natural turquoise called chalk can be scratched easily and can have a hardness of around 3. … Stabilizing processes can be used the bring the hardness of low quality turquoise up to a 3.5 or more. Quality natural stones have a hardness between 5 and 6 without any help."
So, you can see there is a big range. I also read that the closer to the surface the harder. That statement makes me imagine that some mature source that has been mined for a long period of time likely could possibly have a lower quality because we have dug down.
Many of the turquoise dealers that we purchase from claim the stone is natural. I don’t know, but artists that inlay the stones and have to cut it can tell by the smell. Most of the time the cutter is who is going to stabilize the stone. You have some different processes.
The process has become more sophisticated, but I think it has been going on for a longtime. I was told a story by an old trader who purchased some stones during the 50s, the next morning when he woke the stones had already started to change color. That seller had apparently soaked the stones in some type of grease.