Does a granite pestel need to be re-grooved?
Just to clarify, the mortar is the bowl and the pestle is the rod. I haven't ever seen a grooved pestle, but the grooves on a mortar will wear off with use. The grooves are useful for holding seeds and the like in place while grinding, but they are not strictly necessary. Spices can actually be ground finer in a smooth mortar than they can with a grooved one since the particles can't get caught in the ridges, however the initial grinding and tapping may take slightly longer to get started as you chase things like seeds around the bowl a little. The rough surface of the granite alone is enough, just adjust your technique as it wears more.