You can see how dusty they get! The rectangular one on the left is called a 'metate', and for it to be a 'working' model it would probably need to be a bit larger. My Grandmother used to describe grinding corn on a metate back in the days when everything was made at home!
And this is my valuable and trusty molcajete. It has great sentimental value to me because it belonged to my beloved Abuelita! It's also the only one I use. In it I grind cumin and garlic. Funny how spices seem to come alive with flavor when ground on a molcajete. Must be something about the basalt rock that interacts. I need to get a much larger one for grinding jalapenos and tomatoes. You'd think by now I had one for that. I don't know why I haven't just gone to buy one yet. Salsas made in a molcajete are divine bliss! Nothing in the world compares to the flavor. The large one in the photo above is pretty much useless to me. I've tried 'curing' it with several different techniques I've read about, but nothing works. It still releases a lot of grit and sediment. It's kind of like cast iron pots, you need to cure them, but once you have a well seasoned one, it will give you a lifetime of use. Must make a shopping trip to Mexico for a big molcajete!