When I was a young kid, 8 or 9, I found a deposit of some very porous volcanic rock. It was one of the bombs that you see from violent volcanic eruptions. All pumice comes from violent volcanic explosions. It's all the gasses that are in the rock and when the pressure from being underground is released the gasses escape. That is what causes the Violent eruptions and all the holes in the pumice.
I wrote a letter to one of the universities in Austin. I sent a Polaroid picture and where I discovered that the deposits. I just basically asked where did it come from? They couldn't exactly tell me where it came from, but they did say it was deposited from one of the glaciation periods. That made a lot of sense years later when I found out where these really huge rocks/boulders came from that were deposited around the Mason area in Texas. Kind of scary to think about how far south the glaciers actually made it down.
Really, about the only thing you need to worry about pumice is where it's sourced. All the
'good' pumice for growing cannabis and edible plants, is mostly silica. Pumice can come from a multitude of sources, it comes out of the earth. It can have all sorts of heavy metals.
I think having pumice in your media is even more important with autos. Anything that contributes to the health of the root system is important, as we all know.
When I got my first bag of BAS 3.0 media, I knew I was
slacking on the amount of pumice in my media!
The all AutoSeeds Grow in January will be with all fresh 3.0 media in 15 gallon pots!