Mineralogical characteristics of Hongsi Inkstones from Linqu in Shandong Province were studied using petrographic observation, infrared spectra, X-ray powder diffraction (XRD) and electron microprobe analysis (EMPA). The inkstone comprises mainly microcrystalline calcite, subordinately quartz and dolomite, and minor hematite, rutile and muscovite. Hematite is the main factor responsible for the differences of colors. Impurities in Hongsi Inkstone, commonly known as stone eyes, stone bars and ink marks, are also composed of calcite as well as minor quartz and dolomite, with the trace minerals responsible for the differences of impurities.