Deterioration of the Globigerina Limestone of the Maltese Islands

The Globigerina Limestone occurs as two types of building stone: the resistant ‘franka’ and the easily weathering ‘soll’. Research on both fresh and weathered samples has led to an understanding of the main differences in these two types of stone. The causes and mechanisms of deterioration have also been established. ‘Franka’ and ‘soll’ differ in geochemical and mineralogical composition and in physical properties. The ‘soll’ is richer in the non-carbonate fraction, which occludes some of the pore space, resulting in a lower overall porosity and a higher proportion of small pores. The ambient local environment, heavily loaded with sea salt, particularly sodium chloride and sulphates, readily induces deterioration in ‘soll’, whereas ‘franka’ tends to resist better in this aggressive environment. The weathering process of Globigerina Limestone in general has been explained as a sequence of steps, from the formation of a thick and compact superficial crust, to the loss of this crust, to the initiation of alveolar weathering. Understanding the deterioration mechanisms of Globigerina Limestone permits criteria for proper conservation treatment to be established.