For the purpose of this post, I am going to focus on one deodorant stone that I have personally tried and researched, Tade Natural Polished Alum Stone. As for all the other crystal deodorants on the market, I am going to do my best to create a series of posts related to the above questions and attempt to review them all.
Tade Natural Polished Alum Stone claims to be 100% natural alum, and act as a body deodorant by reducing sweat causing odor, also relieving razor burn and tightening and lifting skin.
To begin, alum, which is what natural deodorant stones are made of, does occur naturally, and is mined in quarries throughout the world. The difficulty in verifying whether it is natural or not lies in the fact that alum can be synthetically manufactured to form the identical chemical composition as its natural counterpart. However, synthetic alum is far from natural as it is made by reacting Aluminium trihydroxide (ATH) and acid.
So, I based my findings not on the chemical composition, which however is very important, but on the visual appearance of the stone, which my skill set is better suited for as I am not a chemist.
I have discovered that natural alum appears as a white/clear, translucent, crystal stone that contains veins like those found in marble. And, the synthetic alum is visually very similar, except that it completely opaque, and does not contains veins.
The Tade alum stone clearly contains veins, and when I compared it side by side with other crystal deodorants it was significantly more translucent. Therefore I conclude that it is in fact natural. You can see below in the image the high level of translucency, and the clearly visible veins. Additionally, I contacted Tade directly, and they guaranteed me that it is 100% natural and made from pure, natural alum stone, not from synthetic alum.

Well, speaking from my experience, and from the culmination of surveys, the answer is quite plainly – yes. In fact it works very well. However, it is not your traditional, mainstream fragrance loaded deodorant, or your chemical rich antiperspirant. It allows your body to sweat normally and therefore control body temp, but it prevents the bacteria causing odor found in sweat from developing.
I live a very active lifestyle, always moving around in relatively hot climates. I applied the Tade stone to my underarms in the morning after showering, and I remained odor free all day and well through the evening. To say the least, I was very satisfied with the odor preventing effects.
I also have very sensitive skin, and have had frequent allergic reactions to mainstream deodorants. However, the natural deodorant stone did not create any skin irritations. I even applied it to my face as an aftershave and it seemed to relieve razor burn.