The crystal deodorant stones are made from alum. While there are different types of alums, the most widely used form of alum used in the personal care industry is potassium alum (aka, potash alum). The full chemical name of potassium alum is potassium aluminum sulfate.
The most common way to create potassium aluminum sulfate is through a process called hydrometallurgy. In this process, sulfuric acid is combined with bauxite ore (which is, by the way, not produced at all in the US). The reaction between the sulfuric acid and the ore creates aluminum oxide. This is then reacted with potassium sulfate to form potassium aluminunum sulfate.
While potash alum does naturally ocurr in mineral deposits such as alunite and kalinite, the deodorant stones are manufactured in this less-than-environmentally-friendly way, shipping ore from overseas and using toxic chemicals like sulfuric acid. The stone manufacturers claim that alum is a mineral salt, "similar to that found naturally in the earth's crust." Radioactive uranium is also found naturally in the earth's crust--but that doesn't mean you'd want to use it as a deodorant.
So, is the deodorant stone really a problem?
The reason that most people try to avoid aluminum in deodorant is because of its possible link to Alzheimer's disease. While experts have not come to a consensus that aluminum causes Alzheimer's, there is some strong evidence of a link. For instance, in 1988 a truck driver accidentally dumped 20 tons of aluminum sulfate in to a town's drinking water. Now, over 20 years later, they are finding a higher incidence of Alzheimers in the people of this town that were exposed to the aluminum in the drinking water. Many people point to the fact that aluminum is found in high concentration in brain matter affected by the disease. But while there is plenty of strong circumstantial evidence, researchers are still trying to find out if and how aluminum compounds work within the brain to create the plaques and tangles associated with Alzheimer's. Because not everyone exposed to aluminum develops Alzheimer's, many experts believe that some people who are genetically predisposed to Alzheimer's are particularly suseptible to aluminums. That it acts as a catalyst in the process that creates plaque in the brain. As a precautionary measure, many doctors such as popular web guru and natural health expert Dr. Mercola suggest avoiding aluminum as much as possible.
The common aluminum compounds in anti-perspirants have another risk. Chemicals like aluminum chlorohydrate are estrogen mimickers that can throw off the body's delicate hormonal balance. While no evidence suggests that alum carries this particular risk, it is a form of aluminum and would carry the same possible link to Alzheimer's. The toxicity of potassium alum is also quite high. There have been cases of people who have died from ingesting only 30 grams of alum...that's only one ounce of product. To give you an idea, an average deodorant stone is about 4 ounces---so if a larger chip off a deodorant stone were to break off and be ingested, it could be lethal (especially to a child).
The bottom line is, that while using a deodorant stone is probably better than using a conventional anti-perspirant, it's not aluminum-free and it still poses a possible Alzheimer's risk and contributes to background toxicy in the body.
Want more info? Be sure to check out our follow up article: http://chemicaloftheday.squarespace.com/most-controversial/2010/3/8/exposing-more-truths-about-alum.html