Nice sleuthing! I did order the magnesium oil from Swansons that was all natural somehow and I don't remember how it was harvested/extracted. But it was caked in sodium and just putting a little on my skin raised my blood pressure higher than watching the presidential debates.
So I was curious about it but after losing money on the one form of mag oil, kind of let the idea go. So that's another reason I'm interested in what you're doing. What brand are you using?