Monument grade granite deposits and outcroppings are found all over the world. Often, the attractiveness and thus the marketability of the granite ultimately determine whether it will be quarried. Some granites are so well recognized that they carry with them the name of their place of origin. African black, Swede Rose, and Barrie Grey are examples.
In fact, the Rock of Ages quarry at Barrie Vermont is one of the largest in the world and, not being a great distance away from us here (in Belleville), is well worth a visit. A skyscraper could be built in the bottom of one of their pits and not be seen above ground level!
No heavy explosives are used to quarry monument grade granite. This is to prevent the introduction of fault lines due to blast shock waves. There are a number of ways of quarrying granite. Usually , blocks are separated by means of drilling deep closely spaced holes around and under the portion to be separated.. Then a very low detonation is used to create a fracture just along the rows of boreholes. This is called "shooting the line". The block of granite, which could weigh up to fifty tons or more, is then reduced to more manageable sizes of ten tons or less by means of driving wedges into intermediate lines of drill holes and forcing a split. An explosive charge is not used at this point because of the increased risk of creating fault lines in the newly separated granite. The resulting blocks are hoisted out of the pit [ . . . or off the mountain or ridge] and trucked to a special mill for cutting and polishing.
Requirements for monumental granite are rigid, and only about half of the quarried granite can be used for monuments. The remainder is used for commercial applications.
Where even low-charge detonations might pose a risk, other methods for separating blocks of granite are utilised. They include drilling and wedging, powerful water jets, operating at thousands of pounds pressure per square inch, or high velocity, 3000 degree (F) jet torches which etch a cut flake by flake. Cuts can also be made using a diamond impregnated steel cable saw or a special wire to drag a slurry of sharp cutting grit to grind a cut. This last method is more commonly used in the mill, however, to cut the blocks of granite into "slices" for shaping into monument tablets
|go back up||LONS||contents|