Assessment of chemical weathering of granite stone monuments using reflectance spectroscopy

Reflectance spectroscopy was applied to assess the degree of weathering of the granite sculpture of Buddha in Gyeongju, South Korea, using diagnostic absorption features of representative weathering products (iron oxides and clay minerals). The relative weathering degree map obtained using reflectance spectroscopy corresponds closely with the visual interpretation of exfoliations and cracks. Eight chemical weathering indices (Vogt ratio, weathering potential index, Ruxton ratio, Parker index, modified weathering potential index, chemical index of alteration, plagioclase index of alteration, and chemical index of weathering) determined on granite specimens from three sites in Korea were compared with the quantitative absorption depths of iron oxides and clay minerals. Relatively good correlations were found for the modified weathering potential index and Parker index and the absorption features of iron oxides and good correlations between the weathering potential index and Parker index and the absorption depth of clay minerals. The work has shown the applicability of reflectance spectroscopy as a new non-destructive technique for assessing the weathering of stone monuments.