Young Learner,
There is a way you could find the voltage generated by your weight on that quartz slab: measure it!
A biologist here in Brasil told me that certain insects, especially some ant species, were attracted by electrostatic fields. I amassed more than 100 rose quartz crystals and built a large circular arch with them using silicone adhesive to steady the individual crystals. This configuration caused the bottom-most crystal to be under the most physical stress owing to the weight above it, and thereby generated a large electrostatic field. The effect decreased all the way to the uppermost "keystone" crystal at the top center of the arch. I set the arch out in my yard and waited. Soon a large swarm of army ants passed through my yard but did not seem to loiter on or around my arch. Later, leafcutter ants carrying leaf parts back to their underground fungus gardens stopped and lingered at the base of the arch. For weeks some of the leafcutters milled about the base of my quartz crystal arch. My observations are: the arch was electrically charged, higher voltage at the base. Those ants noticed it and seemed to like it.
Perhaps you could place your quartz slab outside, place a heavy weight on it, and see if it attracts ants.