I do not know exactly what they are made of - some mix of minerals I believe. They work by creating an inhospitable environment for bacteria... so you still sweat, but since it's not the sweat that smells (it's the bacteria that is attracted to the sweat), there's no odor.
It can take some getting used to if you've always used an anti-perspirant/deoderant. I have a few close-fitting, pastel colored tshirts that I can't wear without something over them because the dampness will show up under my arms! Also, it took awhile for the bacteria to get completely eliminated... I did a combo of my old anti-perspirant and the Crystal for a few months before I got rid of the anti-perspirant forever. And if I eat something pungent, like onions or curry, my sweat will smell like that - the Crystal doesn't change that.
I like it and recommend it! It seems healthier to not be blocking my body from sweating, and of course it's much better not to be putting that old toxic stuff on my body everyday. And my shirts don't have that nasty sweat + antiperspirant smell lingernig in the armpits anymore!