In the early days of the porcelain industry in Jingdezhen, the porcelain capital, a single raw material—porcelain stone was used. During the developing process of porcelain industry, the ancestors of Jingdezhen porcelain invented the binary-compositions formulation: mixing porcelain stone and kaolin in a certain proportion to form porcelain raw materials, which greatly improved the quality and efficiency of porcelain production. However, we still do not know why ancient porcelain stones could become suitable raw materials for ancient porcelain making. For this purpose, this article conducted detailed microstructural studies and electron probe mineral composition analysis on porcelain stone samples taken from the rock walls of ancient mining pits in Gaoling Mountain. The results show that the porcelain stone from Gaoling Mountain is a special type of leucogranite, consisting of albite, K-feldspar, quartz, a small amount of biotite, and Fe-muscovite (?), and develops a micro fracture grid structure partially filled by chlorite. This composition and structural characteristics make porcelain stone an early excellent raw material for porcelain production that is easy to mine and process. Combined with the recently published experimental results of high-temperature crystallization of water rich acidic magma, we suggest that the Jingdezhen porcelain stone is a kind of leucogranite formed by dynamic crystallization of a water-saturated granite melt under the lower cooling-rate and lower undercooling degree conditions, with a mineral combination sequence of albite (+biotite) → K-feldspar+quartz →Fe-muscovite (?). Fe-muscovite (?) may be a new mineral, and further research is needed to determine its crystal structure and lattice parameters. The discovery of Fe-muscovite(?) in porcelain stones will help to understand the relationship between changes in the composition of ancient porcelain bodies and changes in porcelain-making formulas, and thus more reasonably infer the onset time of the emergence of binary formula technology.