Bluestone is a natural stone recognized for its distinctive color and various applications in construction and landscaping. While it often features cool, blue-grey tones, the term “bluestone” is primarily a commercial or descriptive name, not a strict geological classification.
Defining Bluestone: A Trade Name, Not a Single Stone Type
The term “bluestone” is primarily a trade or common name used within the construction and landscaping industries. It describes various types of stone that typically share a blue-grey color range, rather than a single geological rock type. This descriptive label is applied to different geological classifications of rock, encompassing over twenty distinct varieties globally. This explains why diverse rock types, formed through varied geological processes, are marketed under this common name.
Common Geological Classifications of “Bluestone”
Many stones marketed as “bluestone” fall into several geological categories, each with unique formation histories. In the United States, particularly Pennsylvania and New York, “Pennsylvania Bluestone” refers to a type of sandstone known as feldspathic greywacke. This sedimentary rock formed from compacted sand and other sediments.
Basalt, an igneous rock from rapidly cooled volcanic lava, is often called “bluestone” in Australia. Some varieties, such as those in Virginia or Belgium, are limestone, a sedimentary rock composed of ancient marine organisms. In other regions, bluestone may also refer to dolerite (igneous) or slate (metamorphic).
Key Physical Characteristics and Uses
Regardless of its precise geological classification, bluestone shares several physical attributes. Its distinctive color ranges from blue-grey to charcoal, and can include shades of lilac, green, brown, or rust depending on mineral content. Bluestone is valued for its durability and density, making it resistant to weathering, erosion, and freeze-thaw cycles. Its robust nature contributes to its longevity and ability to withstand heavy foot traffic.
The stone often has a naturally textured surface, which provides slip resistance, making it suitable for outdoor applications. These properties make bluestone a versatile material for paving projects like patios, walkways, and driveways, as well as for pool coping and surrounds. It is also incorporated into architectural designs for wall cladding, interior and exterior flooring, steps, and fireplace surrounds.
Regional Variations of Bluestone
The interpretation of “bluestone” varies significantly by region, illustrating its role as a descriptive term. In the northeastern United States, “Pennsylvania Bluestone” is a sandstone quarried in Pennsylvania and New York, known for its flat, irregular shapes and diverse color palette. In Australia, “bluestone” commonly describes basalt, an igneous rock from Victoria, though South Australia may refer to slate. In Europe, “Belgian Bluestone” is a specific limestone from Belgium, noted for its dark, dense composition and the presence of fossilized marine life. These regional distinctions underscore that “bluestone” is a culturally and commercially defined term, reflecting the local geology and preferred building materials.