Many laboratory works do not pay any attention to the composition of the mortar and pestle they are using to grind samples for analysis. But like other important things in life, mortar and pestle sets come in a variety of different materials of construction. One should not just use the one that has been used from time immemorial. Some thought should be given as to whether what is being used currently is indeed the "right" choice given the lower limits of detection possible with modern analytical instrumentation.
We are talking about trade-offs. Usually, the harder and more pure the material, the less contamination of the material being ground. And usually this also means a higher price