Blue sandstone, also known as bluestone, is a popular type of sandstone characterized by its bluish-gray color. It has been used as a building material and decorative stone for thousands of years due to its durability, affordability, and aesthetic qualities. But what exactly makes blue sandstone so versatile and useful? Here we’ll explore the unique properties and common uses of this distinctive rock.
What Is Blue Sandstone?
Sandstone is a classic sedimentary rock composed mainly of sand-size mineral grains or rock fragments cemented together by silica, calcite, or iron oxide. The size of the grains, the type of cementing material, and the presence of color-causing minerals like hematite give each type of sandstone unique physical characteristics and appearance.
Blue sandstone belongs to a class of durable sandstones known as quartzose sandstones. It is comprised predominantly of quartz grains cemented by silica, with small amounts of ferric oxides lending the bluish-gray color. It is fairly dense and resistant to weathering. The blue color ranges from pale grayish-blue to deep bluish-gray depending on the specific mineral composition.
Where Does Blue Sandstone Come From?
Blue sandstone formed during the Devonian period around 345 to 395 million years ago. It occurs as sedimentary layers typically interbedded with shales and mudstones. Significant deposits are found in the central United States, including Oklahoma, Illinois, Pennsylvania, Ohio, and West Virginia.
Major quarries producing dimensional blue sandstone can be found in the Appalachian Mountains regions of Pennsylvania, Ohio, and West Virginia. The most famous is the belt of bluestone quarries along the Delaware River in Northeastern Pennsylvania near Easton. Bluestone from this area was used in the construction of the Brooklyn Bridge and Rockefeller Center in New York City.
Properties of Blue Sandstone
The key properties that make blue sandstone so versatile for construction and building projects include:
- Hardness and durability – Blue sandstone is very resistant to weathering and wear due to its dense quartz composition. Its hardness ranks about 6 to 7 on the Mohs scale.
- Compressive strength – It has high compressive strength, bearing heavy loads up to 15,000 psi. This makes it suitable for load-bearing structures.
- Splitting ability – Blue sandstone can be split smoothly along its sedimentary bedding planes into slabs and blocks with chiseling. This quality aids quarrying and stoneworking.
- Workability – Relatively soft compared to granite, blue sandstone is easier to cut, shape and polish using basic masonry tools.
In addition to these technical qualities, the natural blue-gray aesthetic of blue sandstone has made it a popular facing stone choice.
Uses of Blue Sandstone
Thanks to its abundance, physical properties, and handsome appearance, blue sandstone has served many structural and decorative purposes over the centuries. Major uses include:
Building and Construction
Dimensional blue sandstone blocks have been extensively used in building foundations, walls, floors, staircases, and architectural features. Prominent examples where blue sandstone was featured include:
- The blue sandstone cellar walls and foundation of the White House in Washington D.C.
- The Yale University campus buildings in New Haven, CT
- The historic trinity church in New York City
- Buildings in the Michigan State University campus
Landscaping and Masonry
In landscaping, blue sandstone is popular for constructing outdoor paved surfaces, patios, garden walls, pathways, and water features. It is also carved into masonry units like Belgian blocks, curbstones, and cobblestones.
Monuments and Sculpture
Blue sandstone has been a favored material for sculptors and monument construction due to its workability and weather resistance. The luminaries carved out of bluestone include:
- Mount Rushmore National Memorial sculptures
- Components of the Confederate Memorial Carving in Stone Mountain, Georgia
- Gravestones and monuments in many cemeteries across the Northeastern U.S.
Roofing Material
Historically, hand-split bluestone slabs were installed as roof shingles on houses and buildings. In particular, blue sandstone roofs were popular architectural features of 17th and 18th century homes in the Pennsylvania and New England regions. A few of these bluestone roofs can still be seen on vintage buildings today.
Key Advantages
What makes blue sandstone so versatile and useful? Some of its key advantages are:
- Attractive natural blue-gray color
- Extreme durability and longevity
- Dimensional stability and weather resistance
- Strength to support heavy structural loads
- Ease of quarrying blocks and slabs for stoneworking
- Availability throughout the central and eastern U.S.
- Lower cost than rarer imported stones like granite or marble
Disadvantages
Blue sandstone does have some disadvantages to consider:
- Can be damaged by acidic cleaners or salt exposure
- Requires sealing to prevent staining
- Rougher surface than polished stones, so it collects dirt
- Irregular color variations in some deposits
- Limited supply of quarries still actively producing block stone
Conclusion
In summary, blue sandstone is a versatile natural building material valued for its structural strength, weather and water resistance, easy workability with simple tools, attractive bluish-gray color, and reasonable cost. It has served as a foundational construction material since colonial times. While still widely available, many historic quarries are no longer active, so blue sandstone is less plentiful for new projects than in the past. However, its legacy continues to be seen across the country in historic buildings, monuments, infrastructure, and residential architecture.
