QUARRYING, the art of winning or obtaining from the earth's crust the various kinds of stone used in construction, road building and the various manufacturing processes for which rock minerals are employed, the operation being, in most cases, con ducted in open workings. There are two distinct types of quarry ing, one being that employed in the quarrying of what is con stantly referred to as "building stone," for which purpose the stone must be obtained in large unshattered blocks or masses, and the other, the quarrying of stone in rough irregular shapes for road building, concrete aggregate, fluxing and various manufac turing processes, for which purposes it must be broken up, crushed or pulverized in preparing it for utilization. The quarry ing of stone in blocks for use in construction may be further divided, as will be described later, into the several types of quarrying processes that are employed by reason of the character and physical properties of the different types of rock used for "building stone." Building Stone.—According to their general character and composition, building stones are broadly classed as granites, sandstones, limestones, marbles and slates. Under the first of these heads is included a number of crystalline rock species, of igneous origin such as granite, syenite, gneiss, schist, etc., which to the geologist are quite distinct, but which in commerce are all spoken of as granite. They are chiefly composed of one or more minerals of the felspar group mingled with one or more of the micas or with hornblende and usually contain quartz. Sand stones are sedimentary rocks chiefly composed of fragments of quartz consolidated by pressure or cemented into solid rock by silica and oxide of iron. Of these there are many varieties, includ ing bluestone and flagstone used for foot-pavements. Thoroughly cemented sandstones are termed quartzites. Limestones are rocks also of sedimentary origin and consist principally of carbonate of lime or of a combination of the carbonates of lime and mag nesia. Their chief variations are the crystalline form known as marble and the deposit from mineral springs known as Mexican onyx.
The type of limestone used principally for building stone is the oolitic variety, a calcareous-sand rock made up of shells and shell fragments on the sea floor consolidated into a solid mass or in layers and later uplifted to become a part of the land. Slates are mudstones or shales hardened by heat and pressure and rendered fissile by the latter agent. Chemically they consist chiefly of hydrous silicate of alumina. Theoretically, the sedi mentary rock, sandstone, limestone and slate are of a layered formation, although certain limestones and sandstones are mas sive in character, while all granites are massive, and have no bedding or stratification like sandstones and limestones; but all rock masses are usually found to be more or less affected by movements of the earth's crust which occur as a result of its constant readjustment to the cooling and shrinking interior, so that the rocks are divided by cracks or fissures, which are com monly known as joints. In the massive granites these joints, which usually occur in two or more planes at right angles to one another, are of the greatest importance to the quarryman, as they enable him to separate masses of stone with approximately parallel faces. In gneisses the parallel arrangement of the minerals usually coincides with a direction of easy cleavage known to quarry men as the "rift"; at right angles to this direction is usually one less easy parting, known as the "grain." Sandstones and limestones being stratified rocks which have been formed as sediments in bodies of water, whether their beds are found in the normal position of horizontality, or whether they have been tilted and folded by earth movements, the direction of easiest separation is coincident with the original planes of sedimentation and parallel to them. Strictly speaking, the term rift applies only to massive crystalline rocks, the term bedding-plane being a better one to apply to sedimentary rocks.