The rule modern crystal practice runs on: the new moon empties a stone, the full moon fills it. Nothing is done to the stone either way.

It is an internally consistent scheme built on the same waxing-adds, waning-removes logic as the rest of lunar practice, and it gives people a reason to handle their objects on a schedule. Quartz does not change measurably in moonlight. What changes is that twice a month somebody goes and stands outside.