Hey Chef dudes!
Another cooking question for you. I've been given a mortar and pestle but I'm not sure it's usable. It's made of what looks like a volcanic rock type stone. After a few digs at it, I can turn it upside down on a piece of white paper and get a fairly large amount of black grit from it. Is there some type of preparation or "break-in" I can do to it? Do I just sit one evening and grind away for hours on end to "prep it"?
I'm sure eating volcanic rock would tend to wear on the teeth....just a bit. 
Bob
Getting Started Using Lava Molcajete
Your new molcajete must be prepared before first use. They are hand carved by artisans and the surfaces are rough with loose stone and grit that must be removed before it is used to process food. The seasoning/preparation process requires some time and effort but only needs to be done once.
How To Season Molcajete Mortar and Pestle
Unwrap the molcajete and shake or brush off any loose stone or grit. It is recommended that you soak the molcajete and tejolote in warm water for several hours (3-4) before beginning the seasoning process. Soaking will remove dirt, contaminants, and loose sand. Remove the molcajete from the water and allow the piece to dry (a blow dryer makes drying faster!).
The best material to use for the seasoning process is hard dry white rice. The idea is to use a hard gritty material as an abrasive to grind away and remove loose stone and grit and produce a smooth hard surface. Place a small amount of rice in the bowl and begin working it with the tejolote into and over all interior surfaces. As the rice is worked into a fine powder it will be mixed with dark stone grit and take on a dirty gray color. Discard and replace with fresh rice. Continue this process until the resulting pulverized rice is clean and white with no discoloration. The interior of the molcajete should now be smoother and there should be no loose grit. This process may require 30 minutes to an hour and several batches of rice. Rinse or soak the molcajete again to remove any remaining residue. The Molcajete will still be porous but it should no longer produce grit or sand when grinding. Dry thoroughly.
Care of Molcajete
Once your molcajete is seasoned (see above) it should require little cleaning or care. As spices and food ingredients are worked into the bowl the flavors of the spices will penetrate into the stone pores. The molcajete should simply be brushed or wiped out if used for grinding dry spices. After processing moist ingredients for salsa, sauces, or meat rubs you should rinse out the molcajete with warm water. Do not use soap or detergents and avoid using abrasive pads to clean it as you will remove the beneficial seasoning from the pores of the stone. A stiff corn brush is the traditional tool to clean the molcajete with.
The microscopic amounts of basaltic grit that normally wear off the molcajete into the food are said by some to actually be a health benefit.
