It is listed as exotic volcanic ash/clay on the Material Safety Data Sheet (MSDS) and it is non-toxic. It could not be identified when compared to thousands of compounds in Rockwell International's database. It's extremely rare: Only one known source of it in the world.

It was discovered by accident in the 1950s by a search-team doctor. He located lost hikers laying in the desert badly sunburned except where they were laying on this mineral. He put a sample of it in his small fanny pack. When he returned home exhausted, he put his entire fanny pack, with his lunch in it, in the refrigerator and forgot about it. 

Being a busy absent-minded doctor, a week later he checked the refrigerator and discoverd that it was colder and dryer. He opened the fanny pack and found his lunch, with chicken, fruit and vegetables in it, was still in very good shape. He concluded  the mineral had somehow lowered his refrigerator temperature and removed excess moisture to preserve his lunch. And, it had released moisture so the hiker's skin could absorb it. He did some testing and was able to repeat the beneficial performance of the mineral on food and temperatures in refrigeration and Humi-Guard was born.