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Additional recommended knowledge
Bluestone in Britain
British bluestone is a dolerite, and is currently used to make jewelry or knick-knacks.
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.
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 organizing their transportation. If a glacier transported the stones, then it must have been the Irish Sea Glacier. 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 in America
American bluestone is a feldspathic sandstone, which is produced by about 150 mostly small quarries in adjacent areas of Pennsylvania and New York. The Pennsylvania Bluestone Association has 105 members, the vast majority of them quarriers.
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, NY.
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).
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.
This bluestone is made into products as follows: The bluestone is separated from the rock (quarry face) in the quarry by parallel cuts with saws with diamond-tipped blades into large rectangular blocks. Sometimes the stone is lightly blasted to encourage splitting along parallel planes of weakness, delineating the top and bottom of the block. The final products are often made in the quarry, but sometimes massive blocks are trucked to "saw shops" to be finished there, by sawing, by "snapping" or breaking the stone with a guillotine along a line of pressure points, or by splitting along planes of weakness.
The largest volume product is ordinary irregularly-edged flagstone, followed by ashlar. Flagstone belongs to a group of products that require no (or very little) sawing, such as rubble masonry and landscape stone. Two other product groups are classified as Architectural Stone, one group that requires some sawing or "snapping" such as paving stone, wall stone, ashlar, bridge stone, and curbing, and the other group that requires sawing on all surfaces, such as countertops, stair treads, lintels, thresholds, ashlar, sidewalks, and residential walls (veneer). The ashlar can be sawn on all six surfaces, or "snapped" on one or more surfaces with the remaining surfaces sawn.
Bluestone in Victoria, Australia
Australian bluestone is a basalt or olivene basalt, and is quarried by one full-time producer and one part-time producer.
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, Deaf Children Australia and 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.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Bluestone". A list of authors is available in Wikipedia.|