This is a formation of the mineral Lepidolite known as a book due to the way in which the mineral formed in thin layers like the pages of a novel.
Lepidolite is a lithium-rich mica known for its pink and lilac colors. It is a common matrix mineral to Tourmaline and Quartz, providing them with a very aesthetic and glittery base. Lepidolite is mined as a source of the element lithium. Fine-grained masses are sometimes polished into ornaments such as eggs and animal carvings.