As described in the data of this book (see chapter “Porosity and Bulk Density of Porous Materials,” Table 2), the pore structures of minerals and mineral materials can be divided into nanoporous structures (pore size of <100 nm), microscale pore structures (pore size of 0.1–100 μm), and milliscale pore structures (pore size of >0.1 mm) according to the pore size and characteristics. In addition, due to the complex and diverse metallogenic geological conditions of minerals or rocks and the processing and preparation conditions of mineral materials, the types of microstructures are complex, diverse, and rich. At present, it is rather difficult to form a relatively good classification scheme.