High Quality Content by WIKIPEDIA articles! Portland stone is a limestone from the Tithonian stage of the Jurassic period quarried on the Isle of Portland, Dorset. The quarries consist of beds of white-grey limestone separated by chert beds. It has been used extensively as a building stone throughout the British Isles, notably in major public buildings in London such as St Paul`s Cathedral and Buckingham Palace. It is also exported to many countries—Portland stone is used in the United Nations headquarters building in New York City, for example.