chinalie: Portland stone

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The Cenotaph, in Whitehall, London, is made from Portland stone

Portland Stone quarry on the Isle of Portland

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.

The term "Portland Cement" was coined by Joseph Aspdin who produced first in 1824 a hydraulic binder by burning a mixture of limestone and clay resembling the Roman cement and presenting a texture very close to that of the oolitic Portland stone. [1]

Contents

1 Geological Information

2 Quarries & Mines

2.1 Traditional quarrying methods

2.2 New quarrying methods

3 Portland Stone Buildings

4 Memorials

5 Vertebrate fauna

5.1 Ornithischians

5.2 Saurischians

6 See also

7 References

8 External links

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Geological Information

Portland stone formed in a marine environment, on the floor of a shallow, warm, sub-tropical sea probably not too far from land (as evidenced by fossilized driftwood, which is not uncommon). As seawater was warmed by the Sun, its capacity to hold dissolved gas was reduced, consequentially, dissolved carbon dioxide (CO2) was released into the atmosphere (as a gas). Calcium and bicarbonate ions within the water were then able to combine, to form calcium carbonate (CaCO3) as a precipitate. The way that in hard water areas, lime scale builds up in a kettle, might be considered to be a loose analogy of the process. Calcium carbonate is the principle constituent of most limestones. Billions of minute crystals of precipitated calcium carbonate (called Calcite) accumulated forming lime mud (called micrite) which covered the sea floor. Small particles of sand or organic detritus, such as shell fragments, formed a nucleus, which became coated with layers of calcite as they were rolled around in the muddy micrite. The calcite gradually accumulated (by accretion) around the fragments of shell in concentric layers, forming small balls (of less than 0.5mm diameter). This process could possibly be likened to the way in which a snowball grows in size; the more it is rolled around in the snow. Over time, countless billions of these balls or, more correctly; "ooids" or "ooliths" became partially cemented together (or lithified) by more calcite, to form the oolitic limestone we now call Portland stone. Fortunately, the degree of cementation in Portland Stone is such that the stone is sufficiently well cemented to allow it to resist weathering but not so well cemented that it can't be readily worked (cut and carved) by masons, this is one of the reasons why Portland stone is so favoured as a monumental and architectural stone. [2] Dr Ian West of the School of Ocean and Earth Sciences at Southampton University completed a detailed geological survey of Withies Croft Quarry before the Portland Beds were quarried by Albion Stone plc. [3]

Quarries & Mines

Jordans is part of the Inmosthay Quarry in the centre of the Island, which also includes Fancy Beach. The quarry has been worked since the late 1800s. Albion Stone leases the southern section from The Crown Estate and purchased the northern part of the site in 2006. The majority of the southern reserves lie under the grounds of the local cricket club. To avoid disturbing the site at surface level, the company has applied and received permission to extract the stone using mining rather than quarrying techniques. The reserves to the north will be quarried using the diamond bladed cutting machines, hydra bags and the wire saws to shape the blocks. This process avoids the use of potentially damaging, dusty and noisy blasting as the primary extraction method, thereby protecting the surrounding environment, which has been designated as a ite of Special Scientific Interest (SSSI).

Once quarries have been worked they are then restored. The Portland Sculpture and Quarry Trust was formed in 1983. The Trust is dedicated to preserving a knowledge and understanding of stone and the landscape from which it comes.

The quarry at Bowers has been operational since the late 1700. It has been leased from The Crown Estate since 1979 and in 2002 it became the site of the first Portland Stone mine. Extraction from this site is now completely underground with the original Bowers Mine in the extreme southern end of the quarry and the High Wall Extraction on the eastern and south east boundaries. High Wall Extraction is a series of small mines that extract otherwise wasted stone that sits between...(and so on)