Flint Clay

Flint clay has complicated composition and components, does not have fixed structure and composition, difficultly disperses into water and has low plasticity. The currently known flint clay in China is mostly kaolinite monomineral sedimentary clay with associated dickite or hydromica minerals occasionally. The fluctuation range of Al₂O₃ content and SiO₂ content of the flint clay is narrow. The chemical composition of the flint clay is approximate to the theoretical composition (Al₂O₃/3SiO₂=0.85) of kaolinite, and impurities contained in the flint clay include a few iron-bearing minerals and alkali metal oxides besides free quartz. The flint clay is commonly pure white, light grey, light yellow and dark brown and contains a few brown iron sheet materials after being calcined at high temperature.

The flint clay features volume stability, high strength, low water absorption and so on after being calcined at high temperature. Indexes for measuring the sintering degree of the flint clay commonly include true specific gravity, bulk density, porosity, water absorption, sintering shrinkage and so on. The water absorption of the flint clay with good sintering degree is less than 5%, and the bulk density is more than 2.55g/cm3.