Marble Introduction Part 2 – Extraction and Processing
In the previous post, we talked about what marble is, how it is formed and where it is found. Now let’s discuss how it is extracted and processed.
Extraction (Quarrying) of Marble:
The main important factors to consider when selecting a marble quarry are the accessibility of the marble from the crust, its quality and color and other environmental factors. After the suitable area is determined by processes such as core drilling, ground penetration radar, or visual observation, the topsoil is removed to prepare the area for the actual extraction process.
There are various methods used to extract the marble. The suitable method and how it will be applied is chosen for each site to minimize waste and optimize extraction process with greatest efficiency, but this doesn’t mean the mining companies reinvent the wheel each time. There are common practices that are used all the time for a particular region.
One common method of mining is drilling and blasting, although it is a relatively older method and has been outdated considerably. It is basically opening a predetermined pattern of holes in the main marble deposit, in which explosives are placed. When these are detonated, they break up the large body of marble deposit into smaller pieces which are separated from the main body of the deposit, and expose large distinct rock segments which will be easier to work on and process. But the disadvantage here is that it produces a lot of waste and can produce unwanted fractures. Each block usually weighs about at least 10 to 15 thousand tons or greater, which of course varies all the time. Another common method is wire cutting, for initial removing of marble blocks from main rock body. For this, strong thin wires that include diamonds can be used but chainsaws or circular saws are also other options. The proper method to choose depends mainly on the characteristics of the marble. For initial removing marble blocks from mother rock, drilling and blasting is relatively older method, which has gradually been replaced by cutting methods. The cutting methods have the advantage of generating less waste and not having negative environmental effects of explosions. Underground mining methods are also possible depending again on the quality of marble, volume to be removed and the area to be disturbed and the slope of cut if open excavation was used. After the main separation, wedges, hydraulic jacks, airbags can be used to further separate the blocks.
After that these separated large blocks are further broken and cut into smaller blocks or thin pieces called slabs, for making them ready for transporting to processing facility. It is important to minimize waste at this stage, while cutting and shaping the blocks.
The quarrying and extraction operations described above with just a few sentences are actually long and slow processes which can take months,, but as the equipment and technology improve, durations are always improving.
The blocks are then loaded to trucks with cranes and transported to the processing site or ports for shipping and then again to a processing site.
Processing of Marble:
The large blocks are sawcut into smaller blocks or divided into slabs with diamond saws which ensure precision and efficiency. Experience in choosing exactly where to cut is important for the final product quality. The equipment used include gang saws which are large machines with multiple blades, block cutters which are single smaller blades, CNC machines, water jets. The last two are rather used for finer cutting and shaping into more complex forms.
After this step, final shaping and fine finishing of marble surfaces are performed. This step is important to give the stone its appealing look and expose its prominent features such as its veins. It involves polishing to obtain shiny surfaces, honing for matte finishes, flaming or sandblasting for various textured finishes. Resin or epoxy may also be applied to fill cracks or pores and improve strength of marble. Some thin slabs may also be reinforced with mesh backing.
