Geology of Malta

[1][5] The oldest exposed rock layer of Malta is the Lower Coralline Limestone Formation (Maltese: Żonqor), which is of Chattian age (~28–23 million years old) with a maximum thickness of 162 m.[1] The unit is exposed on the lower parts of cliffs in the south-west of the archipelago such as at Dingli, and also along rifts, particularly near Mosta and Naxxar.

[6] It is this formation of which the Azure Window, a spectacular coastal rock arch, popular with tourists and film-makers, was composed, prior to its final collapse in 2017.

It is divided into three members, the lower, middle and upper, with the boundaries between them being hardgrounds, representing the effects of further seabed exposure.

Exposed to the air, the stone takes on a rosy colour, which browns with the formation of a protective patina.

[4] The Maltese Lower Globigerina Limestone has been designated by the International Union of Geological Sciences as a Global Heritage Stone Resource.

The Blue Clay (Maltese: Tafal) is a blue-gray mudstone of Langhian to Tortonian in age (~15–10 million years old) measuring up to 65 m thick.

[8] The Greensand (Maltese: Ġebla s-Safra) is a glauconite-bearing sandstone of Tortonian age (~10–7 million years old).

It is generally very thin, a few tens of centimetres in most areas, with a maximum thickness of 11 m. It is friable and therefore unsuitable for building purposes.

The top layer, the Upper Coralline Limestone (Maltese: Qawwi ta' Fuq), is the youngest formation of Messinian age (~7–5 million years old) and is around 140 m thick.