Importance of optical microscopic investigation in provenance studies and quality characteristics of both historical and natural lower globigerina building limestone of Malta

Abstract

Several megalithic architectural structures dating to the Neolithic Period as well as many early Baroque buildings were constructed from limestone extracted through open-pit mining from the Lower Globigerina Limestone of the Maltese Islands (Bianco, 2018). The Lower Globigerina Limestone Member is the oldest member of the Globigerina Limestone Formation, widely cropping out in the Maltese Archipelago. It is composed of massive, pale yellow in colour limestone that contains tests of globigerinid planktonic forminifera (Pedley, 1974). Limestone quarried from this member has been used as a building stone since time immemorial (Bianco, 2017). Being soft and porous and constantly exposed to atmospheric influences and weathering, the subsequent deterioration of this limestone significantly damages historical monuments. Different methods are used to study its properties, one of which is optical microscopic investigation (thin-section analysis) (Bianco, 2017, 2018). The objective of thin-section analysis is to investigate the texture, porosity and permeability, important properties of a given limestone, which have a bearing on its durability and weathering characteristics. Such investigation is particularly useful when rocks are fine-grained or strongly weathered (Dreesen et al., 2006).