I tried using straight coir to root clones, since I had it hanging around anyway, and it really DIDN'T work. I figured it was the pH, and started experimenting around with that, but found no answer there. It still is very good for transplanting, and mixing with soil with cannabis, but not for the rooting.
I saw that article about the asbestos in vermiculite, and don't look now but auto brakes are coming back with it in an altered form. It was always a great insulator, and material for heat blocking, only if you breathe tons of the dust, then it's like a shiny version of coal miner's black lung. Still a huge shiny mountain in Copperopolis where they shut down the mine.