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Bluestone is the name given to a form of dolerite which appears blue when wet or freshly broken.
Stonehenge
The bluestones at Stonehenge were placed there during the third phase of construction at Stonehenge around 2600 BC. There are about 80 of them and they weigh about 4 tons each. They are believed to have been brought from the Preseli Hills, about 250 miles away in Wales. Generally speaking, the term 'Bluestone' is a quarrymans name for a whole variety of rock types and is stictly not a petrographic name. However, as has already been stated,the rock type known as dolerite is often called by this name. (as is found in the 'bluestone' quarries of Prospect, in western Sydney, NSW Australia)
Pennsylvania and New York
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.
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).
The term "bluestone" is derived from a deep-blue-colored sandstone first found in Ulster County.
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 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.
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.
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.
It is a unique commodity of particular value to the economy of Susquehanna County, Pennsylvania.
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