ABSTRACT

The paper discusses the chemical-physical-petrographic features and decay processes of San Nicola Church (11^th−14^th century) building materials, one of the most representative Medieval Churches in Sardinia, stylistically attributable to the Romanesque architecture. The monument was built up into two stages and shows a characteristic size uniformity of the ashlars. The masonry is mainly made up of rhyodacitic pyroclastites belonging to the Sardinian Eocene-Miocene magmatic phase (38–15 My). These volcanic rocks were widely used in Medieval architecture for the excellent workability, but its minero-petrographic features greatly favor the decay, due to the action of chemical-physical alteration processes. Although the alteration degree and macroscopic forms of decay vary from zone to zone in the monument, according to the different compositional features of the volcanic stones, weathering and exposure condition, the pyroclastic rocks are generally affected by greater alteration than other igneous lithotypes, due to their petrographic-volcanological characteristics (e.g., low-medium welding grade, medium-high porosity). The results concerning mineralogical and petrographic features, respectively, carried out by the application of X-Ray Powder Diffraction (XRPD), Optical Microscope (OM), and Scanning Electron Microscope (SEM) techniques, both on fresh building rocks and associated alterations, are here presented and discussed. Furthermore, the relationships between fresh pyroclastites and alteration processes affecting these rocks will be discussed.

摘要

本文讨论了圣尼古拉教堂的化学-物理-岩石学特征和衰变过程（11 ^th −14 ^th世纪）建筑材料，撒丁岛最具代表性的中世纪教堂之一，风格上归因于罗马式建筑。纪念碑分为两个阶段，并显示出方石的特征尺寸均匀性。砌体主要由属于撒丁岛始新世-中新世岩浆期（38-15 My）的流纹岩火山碎屑岩组成。这些火山岩因其良好的可加工性而被广泛用于中世纪建筑中，但由于化学-物理蚀变过程的作用，其矿物岩石学特征极大地促进了衰变。虽然纪念碑内不同区域的蚀变程度和腐烂的宏观形式各不相同，但根据火山石的组成特征、风化和暴露条件的不同，由于其岩相-火山学特征（例如，低-中焊接等级，中-高孔隙度），火山碎屑岩通常比其他火成岩型受到更大的蚀变影响。分别通过应用 X 射线粉末衍射 (XRPD)、光学显微镜 (OM) 和扫描电子显微镜 (SEM) 技术对新鲜建筑岩石和相关变化进行了有关矿物学和岩相学特征的结果是这里介绍和讨论。此外，还将讨论新鲜火山灰岩与影响这些岩石的蚀变过程之间的关系。分别通过应用 X 射线粉末衍射 (XRPD)、光学显微镜 (OM) 和扫描电子显微镜 (SEM) 技术对新鲜建筑岩石和相关变化进行了有关矿物学和岩相学特征的结果是这里介绍和讨论。此外，还将讨论新鲜火山灰岩与影响这些岩石的蚀变过程之间的关系。分别通过应用 X 射线粉末衍射 (XRPD)、光学显微镜 (OM) 和扫描电子显微镜 (SEM) 技术对新鲜建筑岩石和相关变化进行了有关矿物学和岩相学特征的结果是这里介绍和讨论。此外，还将讨论新鲜火山灰岩与影响这些岩石的蚀变过程之间的关系。