From the Temple of Thai Asian cooking site, on the benefits of using a granite mortar & pestle in cooking:
The reason why the granite mortar and pestle has not entirely been replaced is that indeed it does produce a more delicious paste. Instead of grinding up the fresh herbs and spices with a metal blade, these ingredients are pounded to release and meld all of their natural oils and juices. The metal blade merely cuts the ingredients up and mixes them. But the heavy stone pestle pounds the ingredients in a way that an electric device cannot.
Beyond the idea that the pounding of the pestle can be meditative and help to alleviate stress there may be other health benefits of using your mortar and pestle.
Granite dust contains 5 percent potassium, and has associated with it 16 minerals. Granite dust is commonly used in organic gardening to take care of mites and other harmful pests. According to Dr. D.C. Jarivs, "I have come to the conclusion that potassium alone is not as effective in producing results as potassium with associated minerals, some of which must activate the potassium" (from Folk Medicine, Copyright © 1966)
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