Cracks can form when a sharpening stone is not used for some time, or if usage precautions are not observed. The main causes are sudden drying or extreme changes in temperature.
Shave off the surface at the cracked part. Cracks get deeper as they get wider, so it is important to do this at an early stage, while the crack is still small. If the stone is used in an extremely dry environment, we recommend keeping it in a plastic bag or a sealed plastic container, to prevent acute dry-out after use.