Abstract
The dissolution process of the roof tiles affected by crustose lichen Lecidea sp. grown on their surfaces was investigated by means of optical microscope, XRD, SEM and EPMA. Japanese sekishu roof tiles with mineral compositions of quartz >> mullite was selected in this study. The growth of crustose lichen is often observed widespread on the surface of old roof tiles (about 20 years old). The surfaces of sekishu roof tiles are coated by glaze (melted feldspar-like glass), hence difficult to be affected by normal chemical weathering. However, the decomposition effects of them coated by crustose lichen is possibly mainly due to the biological activities. In this study, the lichen-roof tile interfaces were observed in detail. From the optical and electron microscopic observations, while chemical erosion and physical destruction caused by lichen activities were clearly found on the interfaces, characteristic growth of secondary clays was not recognized on them. In addition, chemical composition images obtained from EPMA do not indicate any leached or precipitated layer as protective weathering crust. From the overall observations it can be concluded that the dissolution progress of the surface of the sekishu roof tiles caused by crustose lichen continues without rate-decrease.
