Victor Horner, age 13, of Birmingham, AL., for his question:
HOW DO YOU QUARRY STONE?
Quarrying is a method of taking large, solid blocks or broken masses of stone from the earth and preparing them for construction projects. Stone is quarried by one of three methods: the plug and feather method, the explosive method or channeling by machinery.
In using the plug and feather method, it was found that rocks can be split along smooth lines by exerting constantly increased pressure evenly on all parts of the rock's surface. With this pressure, workmen can break the rock into any size and shape.
The chief tools are a plug or wedge, which is flat on its two opposite surfaces, and two pieces of steel, called feathers, which are rounded on one side and flat on the other.
The first step is to drill a series of small holes about three quarters of an inch in diameter into the rock in a straight line. The wedge is placed between the two feathers and all three are inserted in a hole. When all the holes are filled, the workmen drive the wedges and feathers downward and split the rock.
The mass of rock that is broken off is turned over to other workmen. They split the rock into smaller pieces by plug and feather method, or with hand tools.
The explosive method is generally used to break off huge masses of rock from their place in the earth. Strong explosives are best if crushed stone is desired. Crushed stone is widely used in paving roads and making concrete.
When larger, more regular stones are needed, a milder explosive is used in the operation.
Most large quarries use a channeling machine to make the first cut into a solid bed of rock. It looks like a small locomotive with long chisels on the sides. The machine moves along a track on top of the rock and forces the chisels downward.
Gradually, the chisels cut the rock to any depth from one to 10 feet. The rock is then broken off by blasting or by the plug and feather method.
In both the strong and milder explosive methods, holes are drilled deep into the solid mass. The explosive is put into the holes and set off by slow burning fuses or electric firing. Sometimes hundreds of tons of stone are forced out of the earth in a few huge pieces.
Quarries in the United States are constantly being opened and shut down. In the early 1980s, more than 5,800 quarries were in operation. These included about 3,200 limestone and dolomite quarries, 500 sandstone, quartz and quartzite quarries, 800 graphite quarries and 60 marble quarries.
About one billion tons of stone are quarried annually in the U.S. Crushed stone make up most of the total production.
Some quarries are dug into the sides of mountains. Most are open at the surface. A quarry may be over 100 feet deep and many times that in width.