I wasn't implying that you carry an M&P, but I suppose that there must be a way to improvise. Mine is a marble one; not very portable. I may just look around and see what could be small enough for the palm of the hand.
I've got a marble one at home, along with a wooden one, but a you say, they're too big for the field unless car camping. A palm-sized version would be cool!
I think it's a brilliant idea to improvise one, MoBOB. I never really thought of it until you posted earlier. I use rocks all the time to crack open black walnuts and hazel nuts. I don't know why I never thought of using the same process for whole spices. DOH!
I had a similar thought about finding a tiny micro grater. Freshly grated cheese, nutmeg, garlic.... I'm going to end up with my old backpack again if I'm not careful. LOL! Perhaps I'll save this idea for serious camp cooking trips.