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 quarrier’s.
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 Arcadian 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 counter tops, 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.