Limestone replacement in restoration : the case of the church of Santa Maria (Birkirkara, Malta)

Abstract

The Church of Santa Maria is one of the finest examples of seventeenth century heritage monuments in the Maltese archipelago. The provenance of limestone used in the restoration works is different from the original heritage fabric. It is obtained from a quarry located 5.2 km south of the church whilst the original source of the limestone, according to tradition, is from an area 2.2 km north of the monument. This petrological study concludes that although both extracted from the same geological formation, there are physical, textural, geochemical and mineralogical differences even over a distance of 7.4 km. The limestone used in replacement is more resistance in terms of compressive strength and is less porous. Although having same principal non-carbonate oxides, the quantitative variations in the geochemistry and the mineralogy are indicative of qualitative differences between the two lithotypes; they are diagnostic indicators of the provenance of the limestone.