MICROSCOPIC CHARACTERISTICS OF PETROGRAPHY AND DISCUSSION ON WEATHERING MECHANISM OF FANGSHAN MARBLE IN BEIJING

Marbles, quarried from Dashiwo town of Fangshan district in Beijing, are employed by many famous stone cultural relics in Beijing. Microscopic characteristics of petrography of white marble and greenish white marble are studied, using the methods of thin section microscopic observation, X-ray diffraction(XRD), X-ray fluorescence(XRF), scanning electron microscopy(SEM) and electron probe test. The fresh marble samples are taken from the quarry. The weathered samples are the debris of broken stones from the historic buildings. Results confirm that the main mineral of the marble is dolomite. Part of the marble contains quartz. Based on image processing software, the particle size distribution of the white marble and greenish white marble are calculated after statistical analysis. On this basis, the weathering mechanism of the marble is analyzed from the view of the temperature change, dissolution due to acid rain, water erosion and the salt crystals along microcracks. The above study can provide a scientific basis for restoration and protection of the marble cultural relics.