"Bluestone" is a colloquial term that usually refers to sedimentary rocks, like sandstone or limestone, that appear blue-gray in color. The most common types of bluestone consist of sediments that underwent millions of years of compression to become stone. This attractive stone commonly serves as a basic building material for homes and businesses.
North American bluestone generally consists of limestone or sandstone, both of which form underwater through the deposition of the granular remains of other rocks and minerals. Over time, geological pressure and heat compress these deposits into solid layers. Sedimentary rock often contains fossils, because the pressures and temperatures required for its formation are not usually high enough to destroy animal remains. The distinct layers typically found in sedimentary rock also allow geologists to identify and study environmental changes over millions of years. In England, the term "bluestone" can refer to various types of igneous rock, which forms when magma cools beneath the Earth's surface.
When wet or freshly cut, sedimentary bluestone usually appears blue. However, it's also available in many other colors. Although it's not as hard as granite, it's a fairly durable stone that is quite resistant to cracking. In addition, it's relatively easy to process it into slabs of a desired size; this is one of bluestone's most attractive features as a building material.
Bluestone is ideal for many building and landscaping applications. It's often used outdoors for pavement or stepping stones, as well as for flooring, pool copings, wall veneers, countertops, tables, fireplaces and architectural facings. Some companies also offer gravel formed from crushed bluestone.
Bluestone is easily honed, sanded, rubbed or treated thermally to achieve the desired appearance and texture. Flamed, cleft, split-face, tumbled and sawn finishes are all achievable on a bluestone work piece.
In America, Pennsylvania and New York feature heavy deposits of bluestone. Mined bluestone is often named after the area from which it came. For example, stone mined in Shenandoah Valley is called Shenandoah Valley bluestone, while stone mined in the Catskills region of upstate New York is called Catskill Mountain bluestone. Dolerite, an igneous rock mined from the Preseli Hills of North Pembrokeshire in the United Kingdom, is also commonly known as "bluestone."