The book I have from the aluminum manufactures. They claim it's another form of aluminum. If antiperspirants contain aluminum, the crystal may be more dangerous since they soak into the skin like a dye. Read Dr. Mercola's article on the Crystal and see for yourself. I know many of us get attached to our body care products but the crystals have not shown enough safety data. The FDA considers antiperspirants a drug and are grandfathered to be use on the market.
With the test equipment available today it is very sophisticated and can detect the tissue damage. If these products were new they would not be allowed on the shelves by today's standards without a Dr's Prescription.