I am analyzing a Scanning Electron Microscope (SEM) on high plastic silt that has been treated with cement. During the examination, I observed a recurring shape across some of the images, which appears to be a particle with a diameter of nearly 20 microns. Could it be a hydration product, or an aggregation of silt particles, or any other foreign material? Could any researchers/ experts shed light on this? It would be a great help. I'm new to analyzing SEM images, so please bear with me if my question seems silly.