Polarized light photomicrograph a 30-µm-thick “thin section of rock. In this case a fossilized bryozoan colony in a limestone from the US. The image shows a detail of the structure of the colony and of the skeleton of bryozoa, with polygonal cavities filled with carbonate. Sample kindly provided by Denise Harrison. I like to disclose the secret beauty of small thin pieces of common or semiprecious rocks when seen with the polarizing microscope. The rock samples are from my geological research, or have been acquired/collected on purpose for aesthetic photography.