1 Introduction

The Natural Stone Council (NSC) is a collaboration of businesses and trade associations that have come together to promote the use of Genuine Stone in commercial and residential applications. By pooling resources, their goal is to increase the understanding of, preference for, and consumption of these natural products. Trade associations affiliated with the NSC include Allied Stone Industries, Elberton Granite Association, Indiana Limestone Institute, Natural Stone Institute, National Building Granite Quarries Association, and the National Slate Association.

Recognizing that green building was becoming a permanent element of the marketplace, the NSC established a Sustainability Committee made up of key industry members to elevate the issue of sustainability within the industry and provide a body responsible for planning and implementing relevant initiatives. In 2007, the NSC Sustainability Committee engaged in a partnership with the Center for Clean Products (CCP) at the University of Tennessee to assess current industry operations relating to dimensional stone production. Prior to this evaluation, the environmental implications of stone extraction and fabrication processes had received little attention compared to other industries. In particular, life-cycle inventory (LCI) data on natural stone products was limited, not well documented, and out-of-date. This information gap was partially due to the size and varying scale of industry members, the vast diversity of products and materials produced, and the global distribution of stone quarrying activities. As such, this work presents the most comprehensive survey to-date of the natural stone industry’s practices.

Provided in the following text are the results of the first phase of a three-year project launched by the NSC to benchmark and improve the environmental profile of the natural stone industry. Specifically, the information that follows is an initial LCI characterizing granite extraction and production operations in North America. These data will serve as a baseline from which industry best practices can be identified, comparisons to competing products can be made with regard to environmental considerations, and future research can be prioritized.

2 Granite Quarrying and Processing Operations

2.1 Granite

Granite is an intrusive igneous rock which is widely distributed throughout Earth’s crust at a range of depths up to 31 mi (50 km). Granite’s characteristic grainy structure and strength is the result of many individual crystalline structures which form tightly together as magma slowly cools within large, deeply buried rock bodies known as plutons. True granite contains 20-60% quartz as well as both plagioclase and alkali feldspars of which the former may not exceed general balance. Other minerals such as hornblende and biotite may also occur in granite, accounting for its variety of appearances (Alden 2004).

Commercially, the term ‘granite’ includes a range of other types of non-granite dimension stone including any feldspathic crystalline rocks or other igneous or metamorphic rocks which possess qualities similar to granite’s grainy, interlocking texture. Many variations of granite appear on the commercial market with white, gray, pink, and red being the most common primary colors. Greens and browns are also available as well as darker grays and black.

Commercial granite is the second largest category of dimensional stone after limestone. Granite is currently produced in 17 U.S. states with Massachusetts, Vermont, Georgia, South Dakota, and New Hampshire leading production (Dolley 2007). Its primary uses include curbing, monumental rough and dressed stone, as well as an array of applications throughout the building industry; this study focuses on dimensional granite production. Two general phases of granite production exist: quarrying and processing. Each of these phases is described below.

2.2 Granite Quarrying Operations

Extraction (more commonly referred to as quarrying) consists of removing blocks or pieces of stone from an identified and unearthed geologic deposit. Differences in the particular quarrying techniques used often stems from variations in the physical properties of the deposit itself—such as density, fracturing/bedding planes, and depth—financial considerations, and the site owner’s preference. Nevertheless, the process is relatively simple: locate or create (minimal) breaks in the stone, remove the stone using heavy machinery, secure the stone on a vehicle for transport, and move the material to storage. A flow diagram of typical quarrying operations is shown in Figure 1.

As shown in Figure 1, the first step in quarrying is to gain access to the granite deposit. This is achieved by removing the layer of earth, vegetation, and rock unsuitable for product—collectively referred to as overburden—with heavy equipment and transferring to onsite storage for potential use in later reclamation of the site. After the face of the granite is exposed, the stone is removed from the quarry in benches, usually 8 to 12 feet square extending 20 feet or more using a variety of techniques suitable to the geology and characteristics of the granite deposit. Quarrying
operations typically include the drilling of holes along the perimeter of the bench, followed by either cutting the stone out of the deposit using saws equipped with diamond wire, or by splitting the stone using hydraulic splitters or small explosive charges. Once the bench is cut or split loose from the deposit, heavy equipment is used to lift the granite bench and transfer it to an inspection area for grading, temporary storage, occasional preprocessing into slabs, and eventual shipment from the site. Granite of insufficient quality or size for current demand is stored on-site
for future use, crushed for use in paving and construction applications, or stored for future site reclamation activities.

2.3 Granite Processing Operations

Processing operations include much more variation than extraction. Nevertheless, the general procedures begin with initial cutting, followed by application of a finish, and conclude with a second cutting or shaping step. Due to the array of stone products, the second and/or third steps may be eliminated, specifically when the product will have a “natural” appearance. Figure 2 depicts the fabrication process.

Processing commences with transportation of the (raw) stone from the quarry to the processing facility, as depicted by Figure 2. It should be noted that this step may consist of multiple transportation steps; prior to reaching the doors of the facility, the stone may be transferred to a number of vendors or distribution locations worldwide. Additionally, some granite (blocks) may have been cut into slabs before reaching the main fabrication plant. These are most commonly sliced to a thickness of 3/4 in (2 cm) or 1-1/4 in (3 cm) in lengths of approximately10-12 ft and widths around 3-5 ft. The route that the stone takes through the plant therefore depends on its physical state upon arrival, as well as the product to be produced.

The first step of the process is a primary cutting or shaping of the material. This is typically accomplished for granite using a circular blade saw, but a diamond wire saw, a gang saw with steel shot, or a splitter can also be implemented. When operating a circular or diamond wire saw, a continuous stream of water over the saw is required in order to dissipate heat generated by the process; sufficiently-elevated temperature can cause major machine and material damage. Natural-faced products, such as veneer or flooring, may be completed with this step, while other products require a finishing application, secondary cutting, or both.

An array of finishing applications exists, and each uses specific types of equipment to accomplish the resulting appearance. Polished or honed finishing is frequently given to granite products, but thermal finishes are also common. The former is applied manually and/or mechanically through the use of polishing pads, while thermal finishes are applied with a flame or blow torch apparatus.

A secondary shaping step may be necessary if the product includes any features or custom size or shape. As with primary cutting, a circular blade saw as well as a diamond wire saw are the most common tools implemented for granite. High-pressure water, a CNC (computer numerical control) machine, or a splitter also may perform the shaping. Cooling water is again necessary for large circular and diamond wire saws, as well as for cutting with high-pressure water and a CNC. Splitters are simply guillotine-like machines and are operated hydraulically.

Once a product is completed, it is packaged and stored for shipment or direct sale. Granite of insufficient quality or size for current demand is stocked on-site for future use, crushed for use in paving and construction applications, or stored for site reclamation activities.

3 LCI Methodology

3.1 LCI Data Collection

Information for this study was acquired through the distribution of a technical data collection tool. This survey was developed by the Center for Clean Products after touring approximately 15 stone quarries and processing facilities located throughout the United States, and through extensive consultation with industry experts and quarry operators. Choosing a diverse array of facilities was key to this process as a broad understanding of stone industry operations was needed to fashion questions that apply to all members. As such, facilities of diverse magnitudes, locations, and products were toured during the beginning half of 2007.

The survey was distributed to granite quarries and processing facilities throughout North America in January of 2008. Responses were received, follow-up conducted, and the resulting data aggregated and analyzed in the period from March to July 2008.

3.2 Quality of LCI Data Set

The dataset presented in this report represents approximately 700,000 tons of quarried granite and nearly 175,000 tons of dimensional granite products generated in North America. Data also reflects a diversity of operations with respect to size and location. Respondents indicated annual quarry production ranging from approximately 400 tons to 240,000 tons, while processors reported a range of roughly 90-55,000 tons/year. Quarry data were submitted from companies located in 71% of the 17 states containing active quarries in 2006 (Dolley 2007), as well as two Canadian provinces. Reporting processing facilities are located in 17 states and one Canadian province

3.3 LCI Boundaries

3.3.1 Granite Quarry Operations

The LCI for quarry operations includes the inputs and outputs for each of the processes depicted in Figure 1. Specifically, processes and operations represented in the inventory presented in this report include:

• Removal of overburden using heavy equipment
• Transfer of overburden to on-site storage
• Quarry operations required to remove stone from deposit including drilling, cutting, splitting, and use of explosive charges.
• On-site transport of stone using heavy equipment
• Transport of scrap stone to on-site storage
• Onsite generation of energy and compressed air
• Capture and treatment of wastewater
• Upstream production of energy and fuels

Equipment and ancillary materials (e.g. drill bits, maintenance items) are listed in Tables 5 and 6 but have not been included in this inventory.

3.3.2 Granite Processing Operations

The LCI for granite processing operations includes the inputs and outputs for each of the processes depicted in Figure 2. Specifically, processes and operations represented in this portion of the inventory include:

• Primary shaping of stone into large, less-refined pieces, such as slabs or veneer
• Application of a surface finish or texture
• Secondary shaping, including hand detailing, of stone into specific products
• Packaging of finished granite products or slabs for shipment
• On-site transport of stone using heavy equipment, such as forklifts
• Transport of scrap stone to on-site storage or reclamation
• Onsite generation of energy and compressed air
• Capture and treatment of wastewater and other waste materials such as dust
• Maintenance activities for processing machinery and heavy equipment
• Upstream production of energy and fuels

Light equipment and materials (e.g. drill bits) are listed in Tables 5 and 6 but have not been included in this inventory.

Since a fabrication facility often processes more than one stone type, each facility was categorized as a “granite” facility if the majority of their production was indicated to be granite. Under this condition, 84% of respondents who are labeled “granite” processors indicate that at least 75% of their production is granite. The majority of the remaining 16% claimed that granite composed 60-70% of their production.

 

References
Alden, Andrew. 2004. Granite. About.com: Geology.
https://www.thoughtco.com/igneous-rock-types-4122909
Dolley, T.P. 2007. Stone, Dimension. USGS 2006 Minerals Yearbook. Vol. 1, Metals & Minerals.
http://minerals.usgs.gov/minerals/pubs/myb.html