Characterization and Chemical Differences of Silica Occurrence within Petrified Wood from Çamlıdere-Kızılcahamam, Ankara (Central Anatolia, Türkiye): Inferences on temperature, pressure, and environment by Confocal Raman Spectroscopy

Petrified woods are not only crucial for the cultural heritage but also important for understanding the volcanology， sedimentology， paleoenvironment， paleoclimatology， paleoecology， paleogeography， paleovegetation， paleobotany and palynology of the region. Although the mineralogy and formation of the petrified woods are well understood， there is a lack of detailed bond characteristic explanation of silica minerals. For this purpose， we have carried out a detailed mineralogical， petrographical， and chemical study of the petrified woods in the Çamlıdere-Kızılcahamam to unravel the detailed characterization of the bond structure of silica and constrain the reason for differences within the Raman peaks. The petrified woods are observed in volcanic rocks and are multicolored （white， beige， grey， and brownish）. The transverse dimensions vary between 2 to 15 cm. The petrified woods of the Çamlıdere have cellular structure along growth rings， and the size of the cell walls is approximately one micrometer. According to the mineralogical and Raman studies， the dominant silica phase is chalcedony， but the pith and cell walls are carnelian in composition. The Raman spectrums of different colored silica formations and core-to-rim measurements reflect the four and six-membered SiO₄ ring in the structure of the silica minerals. The Si content decreases in the cell wall， whereas the Al and Ca concentrations increase slightly. The Raman results show that the temperature remains almost constant throughout the silicification. The minor shift in the peaks at 227-215 and 136-133 cm^-1 may reflect the small pressure changes during the silicification process of the petrified wood in the study area. The existence of the moganite within the crystal structure of chalcedony indicates that the silicification occurred in arid and alkaline environments.