Polarized light photomicrograph a 30-µm-thick “thin section of "Karlsbad Sprudelstein". Karlsbad Sprudelstein is an unusual sedimentary rock with "ooids" (coated grains) made of the carbonate aragonite. It is found in the Czech Republic and is just fantastic under the microscope. When I saw a photomicrograph of this rock in the internet I asked for a small sample in order to obtain this image. Here we see the inner structure of two of these “ooids”, the thin layers of aragonite forming them, and the needles of aragonite cement that keep the grains together like a natural glue. Sample provided by Axel Munnecke. 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.