Portland limestone is the most extensively used imported limestone in Northern Ireland and is also the third most commonly used limestone in Northern Ireland overall. It is a white oolitic mid-upper Jurassic limestone from the South Coast of England, quarried in Portland, South Dorset. It is composed of ooliths (calcium carbonate spheres) and shell fragments and weathers mainly by dissolution, often leaving shell fragments protruding from the surface.
Its pale colour also leaves it prone to rapid soiling, particularly in polluted urban environments. It was used predominantly in Belfast (36 out of a total of 68 buildings featuring Portland Limestone are in Belfast) including several of Belfast’s most prestigious buildings e.g. Belfast City Hall and Parliament House, Stormont.
It is one of the only limestone types that is found in all of the counties, largely due to its extensive usage by the Commonwealth War Graves Commission for memorials, it is also used commonly on banks.