Quarrying refers to extracting materials directly from the surface. Mining is the process of extracting buried material below the earth surface. Thus, quarrying and mining are two different approaches toward extraction. In this passage, we are going to talk about quarrying. To talk about marble quarrying and processing, marble features and characteristics need to be discussed first.
As mentioned earlier, marble is a kind of rock. This type of metamorphic rock, is mainly composed of crystalline calcium carbonate or calcium magnesium carbonate. The word marble derives from the Greek world marmaros. In Greek marmaros means shining stone.
This stem is also the basis for the English adjective marmoreal, which refers to something that is like marble, or someone who is aloof like a marble statue. In addition, the word marble colloquially used to refer to many other stones that are capable of taking a high polish. This is considered as one of the advantages of marble stone.
Marble usually results from metamorphism of sedimentary carbonate rocks, most commonly limestone or dolomite rock. Metamorphism causes variable recrystallization of the original carbonate mineral grains.
The resulting marble rock is typically composed of an interlocking mosaic of carbonate crystals. Primary sedimentary textures and structures of the original carbonate rock called protolith have typically been modified or destroyed.
Metamorphic rocks arise from the transformation of existing rock types. Transformation process of marble is called metamorphism. Metamorphism means change in form. The original rock protolith is subjected to heat temperatures greater than 200 centigrade. Metamorphic rocks make up a large part of the Earth’s crust and form 12 percent of the Earth’s land surface. They are classified by texture and by chemical and mineral assemblage.
Metamorphic rocks may be formed simply by being deep beneath the Earth’s surface, subjected to high temperatures and the great pressure of the rock layers above it. They can form from tectonic processes such as continental collisions, which cause horizontal pressure, friction and distortion. These rocks are also formed when rock is heated by the intrusion of hot molten rock called magma from the Earth’s interior. Some examples of metamorphic rocks are marble, gneiss, slate and quartzite.
Marbles are used principally for buildings and monuments, interior decoration, statuary, table tops, and novelties. Color and appearance are their most important qualities. Resistance to abrasion, which is a function of cohesion between grains as well as the hardness of the component minerals is important for floor and stair treads. The ability to transmit light is important for statuary marble.
Brecciated, colored marbles, onyx marble, and antique are used principally for interior decoration and for novelties. Statuary marble, the most valuable variety, must be pure white and of uniform grain size. For endurance in exterior use, marble should be uniform and nonporous to prevent the entrance of water that might discolor the stone or cause disintegration by freezing. It also should be free from impurities such as pyrite that might lead to staining or weathering.
Calcite marbles that are exposed to atmospheric moisture made acid by its contained carbon dioxide, sulfur dioxide, and other gases maintain a relatively smooth surface during weathering; but dolomite limestone may weather with an irregular, sandy surface from which the dolomite crystals stand out.
The main mineral in marbles is calcite, and this mineral’s variation in hardness, light transmission, and other properties in divers directions has many practical consequences in preparing some marbles. Calcite crystals are doubly refractive—they transmit light in two directions and more light in one direction.
Since marble is a type of metamorphic rock, the use of explosives in the quarrying of marble is limited because of the danger of shattering the rock. Instead, channeling machines that utilize chisel-edged steel bars are used.
This channeling machines make cuts about 5 centimeters (2 inches) wide and a few meters deep. Wherever possible, advantage is taken of natural joints already present in the rock, and cuts are made in the direction of easiest splitting, which is a consequence of the parallel elongation of platy or fibrous minerals.
The marble blocks outlined by joints and cuts are separated by driving wedges into drill holes. Mill sawing into slabs is done with sets of parallel iron blades that move back and forth and are fed by sand and water. The marble may be machined with lathes and carborundum wheels and is then polished with increasingly finer grades of abrasive.
Unfortunately, even with the most careful quarrying and manufacturing methods, at least half of the total output of marble is waste. Some of this material is made into chips for terrazzo flooring and stucco wall finish. In various localities it is put to most of the major uses for which high-calcium limestone is suitable.
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