# Portland stone

- Page: https://taslar.bumba.tr/en/stones/portland-stone/
- Turkish: Portland taşı
- Also known as: Portland limestone, Portland Whitbed, Portland Basebed, Portland Roach
- Kind: Rock
- Classification: Rocks › Sedimentary rocks › Chemical and biochemical
- Hardness (Mohs): 3–4
- Specific gravity: 2–2.4 g/cm³
- Colours: white, cream, light grey, greyish brown (Roach)
- Composition: Oolitic limestone: ooids, small round grains of calcium carbonate, make up about 60% of its volume; the rest is peloids, fragments of mollusc and bryozoan shells, and calcite (sparite) cement.
- Texture: A fine, fish-roe-like texture of ooids mostly under 0.5 mm across, with shell fragments up to 2 cm long. Porosity is high (about 20%). The variety called Roach is full of cavities left by fossil shells that have dissolved away.
- Value ladder: 4/9 step, Fine dimension stone and ore

The white limestone that rebuilt London: the Jurassic stone from Dorset in St Paul's Cathedral, the British Museum and the war graves.

Portland stone is a white or cream limestone quarried on the Isle of Portland, on the Dorset coast of southern England. It formed about 150 million years ago, in the Late Jurassic, in a warm, shallow sea. It is an oolitic limestone, made of small round grains (ooids) that look like fish roe. Easy to carve yet durable, it was used to rebuild London after the Great Fire of 1666 and has been Britain's most famous building stone ever since.

## How does it form?

Portland stone formed in the Tithonian stage of the Late Jurassic, about 150 million years ago, in a warm, shallow sea that covered what is now southern England. As the seawater warmed and lost dissolved carbon dioxide, calcium carbonate began to precipitate. Tiny shell fragments and sand grains rolled about by waves on the sea floor were coated with layer upon layer of calcite, like a snowball, and became round grains called **ooids**. These grains collected together with shell fragments and lime mud and, over time, were cemented into stone. See the [oolitic limestone](/en/stones/oolitic-limestone/) page for more.

In Dorset the formation is about 38 metres thick. Its lower part is a fine-grained limestone with black chert nodules (the Portland Chert Member); its upper part, quarried as building stone, is a thick-bedded, shelly oolitic limestone (the Portland Freestone Member). In this upper part quarrymen distinguish the clean, even-textured **Basebed** below, the more shelly **Whitbed**, and the holey, fossil-rich **Roach**.

## What is it used for?

- **Great buildings:** when Christopher Wren rebuilt St Paul's Cathedral and many churches after the Great Fire of London in 1666, he used nearly one million cubic feet (about 28,000 m³) of Portland stone. The British Museum, Somerset House, the Bank of England, the National Gallery and the east front of Buckingham Palace are also faced with it.
- **Monuments and gravestones:** the Cenotaph in Whitehall (1920) and the headstones of British and Commonwealth servicemen who died in both world wars are made of Portland stone.
- **Around the world:** it was used at the United Nations Headquarters in New York and in early 20th-century buildings in Manchester and Liverpool.
- **Sculpture and carving:** with a hardness of about 3.5 on the Mohs scale it is easy to carve yet durable, which makes it a favourite for monumental lettering and ornament.

## How is it quarried?

The stone has been quarried on the Isle of Portland since Roman times, and it is known to have been shipped to London in the 14th century. Large-scale quarrying began in the early 17th century, when the architect Inigo Jones brought stone for the Banqueting House. The island was linked to the railway in 1865. Today it is worked with diamond-bladed saws, wire saws and underground mining methods that need no blasting; the largest operation is the Jordans underground mine. The cliff quarries on the coast of the Isle of Purbeck also supplied Portland stone for a long time; the Winspit quarry sent stone to London until around 1940. Portland stone has been named a Global Heritage Stone Resource by the International Union of Geological Sciences (IUGS).

## How to recognise it

- It is white, cream or light grey; up close the surface looks covered in small round grains (ooids) no bigger than a pinhead, with shell fragments scattered through it.
- The variety called Roach is full of cavities left by fossil shells and has a spongy, holey look.
- A steel knife scratches it and it fizzes in dilute acid. Because it is porous, a drop of water soaks into the surface quickly.
- It is a light stone (density about 2.0–2.4 g/cm³), roughly a fifth lighter than marble of the same size.

## What determines its value?

The value of Portland stone depends on whether large, sound blocks can be extracted, on the lightness and evenness of its colour, on a fine, regular texture and on how much shell it contains. Whitbed and Basebed, with an even texture and few shell fragments, are the most sought-after building stones because they can also be used for fine carving and sculpture, while the holey Roach is used for rougher work and decorative surfaces. Its association with famous buildings, and the need for the same stone in repairs, keep it in steady demand.

This information is educational, not buying, selling or investment advice. Value varies enormously with quality and treatment.

## Myths and misconceptions

- Myth: Portland cement is made from Portland stone. Fact: Joseph Aspdin, who patented the cement in 1824, named it after Portland stone because once set it looked like that pale limestone. Portland cement is usually made from ordinary limestone and clay, not from Portland stone.
- Myth: Portland stone comes only from the Isle of Portland. Fact: The Portland Stone Formation it belongs to occurs over a wider area of southern England: in the cliffs of the Isle of Purbeck in Dorset, in the Vale of Wardour and Vale of Pewsey in Wiltshire, and beneath the English Channel. The formation's reference section is not even on Portland but at Winspit and St Alban's Head on Purbeck.

## What is it believed to be good for?

This section reports beliefs; it is not health information. There is no scientific evidence for these claims and no stone replaces medical treatment.

- Quarrymen on the Isle of Portland believed that rabbits coming out of their burrows foretold a rockfall, which is why saying the word “rabbit” on the island is still considered unlucky.

What science says: Rockfalls in quarries depend on the stone's fractures, the weather and the way it is worked; saying or not saying a word has no effect. Today the belief lives on mostly as a local tradition: in 2005 even the word “rabbit” on an animated film's posters on the island was changed.

## Did you know?

- After the First World War, the Portland quarries supplied the stone for the Cenotaph in Whitehall and half a million gravestones for the war cemeteries. The Commonwealth War Graves Commission still uses Portland Basebed today.
- The façade of the United Nations Headquarters in New York (1952) also uses Portland stone.
- On the Isle of Portland the word “rabbit” is not said aloud; islanders call the animal “underground mutton” or “long-eared furry things” instead.

## Where is it found?

- Isle of Portland, Dorset, England (Major deposit): The island that gives the stone its name, quarried since Roman times. Today it is worked in the Jordans and Stonehills underground mines and the Bowers, Perryfield and Broadcroft quarries; the island's Clay Ope section is one of the formation's reference sections.
- Winspit and St Alban's Head, Isle of Purbeck, Dorset (Type locality): Reference (type) section of the Portland Stone Formation, fully exposed in the sea cliffs. “Cliff stone” was quarried from the cliff quarries between Durlston Head and St Alban's Head, and the Winspit quarry sent stone to London until about 1940.
- Ringstead Bay, Dorset (Known locality): East of Weymouth; one of the formation's reference sections.
- Chilmark, Vale of Wardour, Wiltshire (Historic source): In this vale the Portland Stone Formation is divided into the Tisbury, Wockley and Chilmark members. Stone from the Chilmark quarries was used for the main structure of Salisbury Cathedral.

## Sources

- [Portland stone](https://en.wikipedia.org/wiki/Portland_stone), Wikipedia
- [Portland Stone Formation (POST)](https://webapps.bgs.ac.uk/lexicon/lexicon.cfm?pub=POST), British Geological Survey, BGS Lexicon of Named Rock Units
- [Portland Stone: a nomination for “Global Heritage Stone Resource” from the United Kingdom (Hughes, Lott, Poultney & Cooper), Episodes 36(3)](https://nora.nerc.ac.uk/id/eprint/511810), International Union of Geological Sciences (NERC Open Research Archive), 2013
- [Stonehills Whitbed: technical data sheet compiled by the Building Research Establishment (BRE)](https://www.albionstone.com/download_file/view/702/430), Albion Stone, 2022
- [Heritage Portland Stone: Understanding the Geology Behind the Name](https://www.albionstone.com/news/heritage-portland-stone-understanding-geology-behind-name), Albion Stone
- [Isle of Portland](https://en.wikipedia.org/wiki/Isle_of_Portland), Wikipedia
- [Portland cement](https://en.wikipedia.org/wiki/Portland_cement), Wikipedia
- [Winspit](https://en.wikipedia.org/wiki/Winspit), Wikipedia
- [Purbeck-Portland “Cliff Stone”](https://www.dorsetbuildingstone.org/purbeck-portland-ldquocliff-stonerdquo.html), Dorset Building Stone
- [Ringstead Bay](https://en.wikipedia.org/wiki/Ringstead_Bay), Wikipedia
- [Chilmark Quarries](https://en.wikipedia.org/wiki/Chilmark_Quarries), Wikipedia


Source: https://taslar.bumba.tr/en/stones/portland-stone/ · Licence: CC BY-SA 4.0