It is interesting to read all these ideas for an eco deoderant as I am always on the look out for a green alternative.  I haven't tried any crystals but over the years I have used pitrock, Weleda and green people deoderant and haven't found them any good.
However, one thing I have found absolutely amazing is using a lemon.  
I don't want to stop myself sweating but I want to stop smelling and I read that cutting a slice of lemon and them rubbing it underarm  apparently stops any whiffs. So each morning for 3 months I have been slicing the lemon and rubbing it under my arm. By the end of the day when I would be a bit pongy I don't smell. 
 
 
My DH is getting a bit peeved off with me thrusting my pits in his face with the question, "does it smell?  That's amazing isn't it?"
One small lemon seems to last a week. I have used a lemon on freshly shaved pits and it doesn't sting very much either.