It appears that Magnesium Direct is the only officially licensed product for the Zechstein Magnesium oil in the US. I have not been able to find any one else, other than Magnesium Direct's DermaMag, whose product has the official "Zechstein Inside" logo on the bottle. Evidently, the Zechstein Inside logo was created by the mine in Europe to help customers know when they are buying the authentic product. As far as I can tell, it only comes from one mine.
I use the DermaMag and it works great. Because it is officially licensed, you know you aren't getting a counterfeit or cheaper substitute.
You can go to there website by clicking magnesium oil