Some marbles have natural vents and fissures. For the most part these are filled during processing and have no effect on the finished product. Usually these materials come backed with a matting for safety in the event parts fall away. Generally if the piece has survived transit and the rigorous polishing process it should be good enough to work with, but occasionally we have to take further measures to stop them opening up during fabrication, transit and installation. Once installed they are of little concern and are part and parcel of the overall desired look.
The pictures show the process of rodding a flipped up piece of marble with fibreglass. This increases its strength and increases safety should the material fail.