from a Google Search:
Tonsil Stones (tonsilloliths) are caused by an accumulation of sulfur-producing bacteria and debris that become lodged in the tonsils. This debris (which can include mucous from post nasal drip) putrifies in the back of your throat, and collects in the tonsil crypts (small divots or pockets which appear on the surface of the tonsils).
When this debris combines with the Volatile Sulfur Compounds produced by the anaerobic bacteria beneath the surface of your tongue, along with the tonsil stones it can also create chronic Halitosis (and other stubborn bad breath and taste disorders).
Important: If you do not have your tonsils then you will NOT (except for rare exceptions)
experience tonsil stones. However this does NOT mean that you should
run out and get your tonsils removed.