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In today’s marketplace, a wide array of natural stones are available for U.S. dimension stone production. These include granite, limestone, sandstone and marble, each with unique qualities of color, texture, physical properties and more. In our 100+ years of producing natural dimension stone at Coldspring, we’ve seen how an understanding of each stone type helps architects and specifiers ensure a beautiful, enduring design. What’s more, insight into quarry and production techniques invariably contribute to successful architectural projects. Here, we provide an overview of the ins and outs of natural stone formation and fabrication to help architects and specifiers create designs that please – and wow –owners.
Basic Formations and Characteristics
The three basic geological stone formations, each with their own physical characteristics, include:
Through erosion, small particles of the earth collect at the bottom of lakes, rivers and streams. A layering effect results; over thousands of years, bottom layers begin to solidify. Sandstone, limestone, onyx and travertine are all sedimentary materials.
Starts as sedimentary, but heat and pressure lead to a chemical change. Examples of metamorphic include marble, slate and quartzite.
The result of the cooling of molten material that is pushed toward and/or through the earth’s surface. This “extrusive” rock is the material granite quarriers are after. In addition to granite, basalt is also an example of igneous.
Granite is a viscous molten material that cools slowly while under pressure and displays anisotropic qualities (non-directional grain structure). Its primary components are quartz—the base material—followed by feldspar and mica.
Pro Tip: Gain an understanding of the various materials to ensure you choose the right type of stone for your project, based on considerations such as indoor or outdoor use, geographical location, freeze/thaw cycles, and more.
Quarrying, Then and Now
For many years, stone quarries were open-shaft and serviced by stiff leg-lifting derricks. Most work was performed with manual labor while light machinery was used for lifting. Quarrying involved freeing single blocks, sized for lifting and distance from the derrick. Derricks had to be moved to various locations, and quarriers were required to move deeper or open new holes adjacent to the original deposit. As equipment and techniques advanced, this method of quarrying became more difficult.
Today, quarries use a “drive-in” approach. Mobile equipment can access all levels of the quarry, allowing for access to parts of the quarry for stone size, color variations and other considerations. Thanks to modern quarry innovations and capacity increases, crews can meet demand.
One of these innovations, the diamond wire saw, opens and develops various areas of the quarry. Cutting both vertically and horizontally, the diamond wire saw can also serve as a portable trimming tool. This flexible tool has replaced the now obsolete use of explosives and jet burners. For softer materials such as limestone and sandstone, the diamond chain saw works quickly and effectively.
Pro Tip: Modern quarrying techniques are vastly different from obsolete methods, offering increased efficiency and sustainability.
Natural stone fabrication is a highly evolved, technically advanced process to turn a rough slab into the finished product. The fabrication process involves meeting and/or completing the following:
- Thickness standards
- Slabbing operations
- Slab finishing methods
- Cut-to-size process
- CNC (Computer Numerically Controlled) production
- Inspection and shipping
Before fabrication, quarry blocks can vary greatly in size. The ideal size measures 5.5 by 5.5 by 10.5 feet and weighs approximately 50,000 pounds. When blocks reach the fabrication facility, they are prepped for the diamond wire saws, which are set for standard thicknesses. These standard saw thicknesses may affect pricing and fabrication time. After the fabrication process of sawing and finishing, the resulting slab’s size measures 5 by 10 feet.
Non-standard block sizes are also available. More project owners are seeing a value in sizing blocks to their specific needs, cutting down on waste.
Each quarry is unique and will yield different sized blocks depending on seams and natural characteristics. The quarrier or manufacturer should be consulted about what piece sizes will best fit the project requirements.
Pro Tip: Custom-sized blocks can help reduce waste on your project. Be sure to consult your stone manufacturer.
With the tremendous influx of foreign materials, it’s more important than ever to be sure your selected natural stone meets ASTM standards. Stone categories have varying physical properties, and different guidelines are required for each. The ASTM standards ensure each stone category, including marble, limestone and granite, has been addressed based on its characteristics and traits.
ASTM C615 is the standard applied to granite. It outlines the minimum values required using a battery of tests. The evaluation includes consideration of structural effects, durability, thermal expansion and more.
To address compressive strength, ASTM C170 provides a baseline to determine a material’s relative strength and weight-bearing capacity. To address the effect differing rock strata have on finished materials, parallel and perpendicular testing is conducted on the bedding plane.
For more information, the ASTM minimum recommendations can be found on the NBGQA (National Building Granite Quarries Association) website.
Pro Tip: Ensure your selected material meets ASTM standards, and remain particularly vigilant when considering international stone.
The Importance of Sustainability Certification
In 2018, the National Stone Council and the American National Standards Institute adopted a sustainability certification standard for natural stone production. Known as the ANSI/NSC 373Sustainable Production of Natural Dimension Stone, the standard provides third-party verification for sustainable quarrying and fabrication practices in the industry. How natural stone is quarried, processed, transported and used has a significant bearing on its environmental impact.
Coldspring is committed to establishing and promoting industry-wide best practices to protect our planet and is dedicated to developing and maintaining resource management and process practices that minimize our impact. To underscore this commitment, Coldspring was among the first companies to be certified under this new standard.
Pro Tip: If sustainably produced products is a priority for your project, be sure to include NSC 373-certified natural stone in your plans.
To learn more about natural stone formation and fabrication and to earn 1 HSW Continuing Education Unit, register for our complimentary “Using Natural Stone in Today’s Architecture: Stone Formation to Fabrication” course.