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Bluestone
From Wikipedia, the free encyclopedia
Bluestone is the name given to a form of dolerite which appears blue when wet or freshly broken.
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Bluestone is a high quality product due to its silica content, compact nature and fine grains. It is used for patios, architectural facings, fireplaces, sills, sidewalks, and other features as well as a basic building material for churches, institutions, homes and businesses.
Bluestone is an evenly-bedded product which tends to exhibit natural horizontal clefts allowing it to be removed in large flat sections suitable for flagstone, curbing, and the like. Where the clefts are less well defined, the stone is removed in blocks which are then taken to processors for cutting and refining.
The refining process for bluestone slabs is called spalling. This process incorporates water and heat to reveal the natural layers of the stone as it was deposited originally. The cutting orientation must be almost exactly along the horizontal layers. The cut slab surface is soaked with water and heated rapidly with a wide nozzle propane torch, breaking off chips of stone along their fault lines.
Many of the sidewalks in New York City were paved with Catskill and Pennsylvania bluestone. It is extremely durable and the quality of the product is not found anywhere else in the United States or Canada.
The bluestones at Stonehenge were placed there during the third phase of construction at Stonehenge around 2600 BC. It is assumed that there were about 80 of them originally, but this has never been proven. The stones weigh about 4 tons each. They are believed to have been brought from the Preseli Hills, about 250 miles away in Wales, either through glaciation (erratic theory) or through humans organising their transportation. Recently the archaeological find of the Boscombe Bowmen has been cited in support of the latter theory, but there is absolutely nothing, in the opinion of some geologists, to connect the finds with Wales in preference to any other European area of Palaeozoic rocks. 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 (see N P Figgis Prehistoric Preseli). There is also a legend of Merlin having miraculously transported the stones himself.
The term 'Preseli Bluestone' is quarryman's name for a whole variety of rock types and strictly is not a petrographic name. At Stonehenge, there are two types of dolerite - spotted and unspotted. The dolerite of the Preselis are plagioclase feldspar. There is no evidence in Pembrokeshire that spotted dolerite (or any dolerite, for that matter) was used preferentailly either for the building of monuments or burial chambers (cromlechs), or for the manufacture of axes. The bluestones may not even have been used preferentially at Stonehenge, and around half of the original stones used in the "bluestone setting" were probably sarsen stones which were later used as lintels.
Bluestone from Pennsylvania and New York is commercially known as 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.
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 Catskills (and Northeast Pennsylvania).
Bluestones from this source are often called Pennsylvania River Rock or variations of this name depending on the market or origin of the stone.
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.
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 a quarry in the Clifton Hill area and used extensively in the 19th century. Because the material was difficult to carve, 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, Victorian College for the Deaf, Royal Victorian College for the Blind, the Goldsborough Mort warehouses (Bourke Street) and Timeball Tower. It was also used extensively for cobblestone roads, many which still exist in some of Melbourne's smaller lanes as well as walls, bridges, curbs and gutters in many of the 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.
It was also sourced in many other regions of the Victorian volcanic plains and used in towns and cities of central and western regions including Ballarat, Geelong, Port Fairy and Portland.