The answer Tony settled on was that it lasts at least a thousand years because it’s made of sandstone which is so soft that it’ll never crack, unlike marble.
This is obvious BS, but in a romantic enough way that I’m not mad about it. I find that there are many granite and blue hardstone mines, so those seem more likely materials to make a rice grinder from.
A Google search seems to suggest that a granite grinder will last 30-40 years, so I guess we have somewhat of an answer.
