Does the silicone substrate have something to do with this?
Reminds me of of the Cheerio Effect of particles at a fluid / air interface. (more here) except these particles are not in a fluid.
Space/Science » in reply to Fractal clumping of Mars Soil
Reminds me of of the Cheerio Effect of particles at a fluid / air interface. (more here) except these particles are not in a fluid.