As many know it is one of my specialties to place trees on slabs. Most folks use man made slabs because of availability and price. Really good natural stones are very hard to get. I know a source in Germany since many years and I am happy to reveal it now. It is Gunter Maintz , the owner of Eifel Bonsai in the vicinity of Cologne, Germany who find these stones. They come from a volcanic region. The water at some wells is warm and contains many minerals. When it cools off the minerals fall out and create these great formations over many years. The colors are strong, but not as orange as on the photographs. The structure is unique and very interesting, obviously natural. I love these stones, especially for spruce and pines. Some of these stones are available.