Just ordered the small (6") version of these granite mortar and pestle. Looked at lots of info and Thai granite was deemed to do the best job.
Found what I needed at my favorite online Thai Supermarket. These guys are great. Been buying from them for years....Sweet Chili Sauce... Vietnamese Pho Ramen...etc.
I understand that you need to "season" the mortar by grinding rice in it first. OK. I have rice. I can do that.