Mineralogy and geochemistry of blue patches occurring in the globigerina limestone formation used in the architecture of the Maltese islands

Abstract

The stratigraphy of the Maltese Archipelago is composed of Oligo-Miocene industrial minerals of shallow marine origin. The Lower Globigerina Limestone Member, the earliest of the three members forming the Globigerina Limestone Formation, had been used as the main building material of the islands since the Neolithic Period. A bluish coloured lithostratigraphic bed, known in the quarry industry as sol ikħal, occurs within this unit. Furthermore, occasionally, large blue patches occur in this member. They were first studied by John Murray whose research was published towards the end of the nineteenth century. This article analyses the mineralogy and geochemistry of sol ikħal and these patches applying XRF and XRD. Whilst the results for the blue patches corroborate and refine the findings of Murray, they differ from sol ikħal. Their SiO2 content is > 10%; for sol ikħal it is < 10%.