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Bluestone is a cultural or commercial name for a number of dimension or building stone varieties, including:
The term "bluestone" in Britain is used in a loose sense to cover all of the "foreign" stones at Stonehenge. It is a "convenience" label rather than a geological term, since at least 20 different rock types are represented. One of the most common rocks in the assemblage is known as Preseli Spotted Dolerite—a chemically altered igneous rock containing spots or clusters of plagioclase feldspar. It is a medium grained dark and heavy rock, harder than granite. Preseli bluestone tools, such as axes, have been discovered all over the British Isles. Many of them appear to have been made in or near Stonehenge, since there are petrographic similarities with some of the spotted dolerites there.
The bluestones at Stonehenge were placed there during the third phase of construction at Stonehenge around 2300 BC. It is assumed that there were about 80 of them originally, but this has never been proven since only 43 remain. The stones weigh between 2 and 4 tons each. The majority of them are believed to have been brought from the Preseli Hills, about 250 miles away in Wales, either through glaciation (glacial erratic theory) or through humans organizing their transportation. If a glacier transported the stones, then it must have been the Irish Sea Glacier. In such event, one might expect to find other bluestones near the Stonehenge site, but no such bluestones (apart from fragments) have been found.
Recently the archaeological find of the Boscombe Bowmen has been cited in support of the human transport theory, while new glacier modelling supports the erratic theory. Preseli Bluestone dolerite axe heads have been found around the Preseli Hills as well, indicating that there was a population who knew how to work with the stones.
A summary which outlines the major aspects of the Stonehenge "bluestone conundrum" has recently been published. A new book devoted specifically to the problem of bluestone provenance and transport concludes that the Stonehenge bluestones are essentially an ill-sorted assemblage of glacial erratics. Research into the origin of the bluestones is ongoing as of 2012.
The best known American variety of bluestone is a feldspathic sandstone, which is produced in hundreds of small quarries in adjacent areas of Pennsylvania and New York. It is also quarried in the Canadian Appalachians near Deer Lake in Western Newfoundland. The Pennsylvania Bluestone Association has 105 members, the vast majority of them quarriers. The other, lesser known, type of American bluestone is formed from a different sedimentary rock, limestone. The limestone is abundant in the Shenandoah Valley of Virginia yet The Frazier Quarry is the only remaining quarry that cuts dimension stone from it.
Bluestone from Pennsylvania and New York is commercially known as bluestone or Pennsylvania Bluestone. These are a group of sandstones defined as feldspathic greywacke. The sand-sized grains from which bluestone is constituted were deposited in the Catskill Delta during the Middle to Upper Devonian Period of the Paleozoic Era, approximately 370 to 345 million years ago. If the initial deposit was made under slow moving water the ripples of the water action on the sand or mud will be revealed. This deposition process may be seen today at any ocean beach in shallow water or in a stream bed where conditions allow it to be observed. The term "bluestone" is derived from a deep-blue-colored sandstone first found in Ulster County, New York.
The Catskill Delta was created from run off from the Acadian Mountains ("Ancestral Appalachians") which covered the area where New York City now exists. This Delta ran in a narrow band from southwest to northeast and today provides the base material for the high-quality bluestone which is quarried from the Catskill Mountains and Northeast Pennsylvania.
As the product became more popular as an architectural and building stone and demand grew, quarrying for it spread throughout south central New York and northeast Pennsylvania. It is a unique commodity of particular value to the economy of Susquehanna County, Pennsylvania. The Starrucca Viaduct, finished in 1848, is often referred to as an example of the strength and durability of Pennsylvania Bluestone as a building material.
Bluestone from the Shenandoah Valley is regionally known as bluestone but a less ambiguous name is Shenandoah Valley Bluestone. The limestone formed during the Ordovician Period approximately 450 to 500 million years ago, but it was formed at the bottom of a relatively shallow ocean that then covered what is today Rockingham County, Virginia. However, the limestone that accumulated in Rockingham County was darker in color than most other limestone deposits because it was in deeper waters exposed to less light. The darker blue color resulted in limestone from this region to be dubbed bluestone and with two sequences measuring about 10,000 ft, it gives the area one of the largest limestone deposits in the world. The stone eventually fades from a deep blue to a light grey after prolonged exposure to the sun and rain.
Given the abundance of the stone in the Rockingham County area, the first settlers used it as foundations and chimneys for their houses. When James Madison University was built, the native bluestone was used to construct the buildings because of its high quality and cultural ties. The Frazier Quarry in Harrisonburg, Virginia Continues to supply JMU with the native bluestone.
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There are two distinct building materials known as bluestone in Australia. Victorian bluestone is a basalt or olivine basalt, and is quarried by a number of companies throughout the state.
In Victoria, Australia, bluestone was one of the favoured building materials of the 1850s during the Victorian Gold Rush. In Melbourne it was extracted from quarries throughout the Inner Northern suburbs (such as Clifton Hill, Brunswick and Coburg, where the Coburg Lake was the source for Pentridge below) and used extensively in the 19th century. Because the material was difficult to work, it was predominantly used for warehouses and the foundations of public buildings. Significant bluestone buildings include the Melbourne Gaol, HM Prison Pentridge, St Patrick's Cathedral, Victoria Barracks, Melbourne Grammar School, Deaf Children Australia and Victorian College for the Deaf, Vision Australia, the Goldsbrough Mort warehouses (Bourke Street) and Timeball Tower. It was also used extensively for cobblestone roads, many which still exist in some of Melbourne City's smaller lanes and more extensively in the 19th Century inner suburbs as well as buildings, walls, bridges, kerbs and gutters in many of those inner suburbs. Some examples of structures that use the material include Princes Bridge and Federation Wharf and Hawthorn Bridge. Because of its distinctive qualities, post-modern Melbourne buildings have also made use of nostalgic bluestone, including the Southgate complex and promenade in Southbank, Victoria and apartments such as the Melburnian.
Crushed bluestone aggregate, known as bluemetal, has been used extensively in Victoria as railway ballast, as road base and road surfacing material, combined with bitumen, and in concrete making.
In South Australia, the name bluestone is given to a form of slate which is much less durable than Victorian bluestone, but was valued for its decorative appearance. The interior of the stone is usually pale grey or beige in colour, but is given attractively coloured surfaces by ferric oxide and other minerals deposited in joints and bedding planes. The slate is laid in masonry with the mineralised surfaces exposed. Bluestone was most popular from about the 1850s to the 1920s, quarried in the Adelaide Hills at Dry Creek, O'Halloran Hill (formerly Tapley's Hill) and Glen Osmond, and a number of other places in rural areas.
Timaru bluestone is an attractive building material, used both historically and to the present. It is a grey basalt similar to Victorian bluestone, quarried near Timaru in the South Island. Bluestone from near Kokonga in Central Otago is also widely used, and is the main construction material (often with facing of Oamaru stone, a local compact limestone) in many of the notable historic buildings in the southern South Island, most of which were constructed during the financial boom following the Central Otago gold rush.
Prominent structures to use this combination include Otago University Registry Building, Dunedin Law Courts, and Dunedin Railway Station. Similar construction using Timaru bluestone was used for Christchurch Arts Centre.
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