We use ground walnut shells instead of sand in our pincushions in addition to wool stuffing. It gives a bit of heft and sharpens pins and needles.
This is a fine grit, akin to sand. It requires an extra layer of fabric or wool to keep it inside the pincushion. Try making a simple insert with scrap fabric to put inside your creations.
We re-use jars from the grocery store to package the ground shells. We encourage you to keep and use your jars as well. It is recommended that you order bagged walnut shells to save shipping costs, and put it in your own saved jars.