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 a “large”(approximately 12 by 8 mm) view of the petrographic thin section. The composite photo shows the incredible structure of Karlsbad Sprudelstein, its “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.