BUILDING STONE, any stone used in the construction of buildings. The stones mostly employed are granite, sandstone, limestone, marble, serpentine, and trap. In order that a stone may be used to advantage for building purposes, it must possess certain physical and chemical properties; these are durability, permanency of color, crushing strength, elasticity, and cheapness. Stones vary greatly in their durability, depending upon their chemical composition, and the purposes for which they are used. As soon as a stone is quarried, it becomes exposed to changes in temperature, caus ing expansion and contraction of its par ticles and ending ultimately in its disin tegration; to the chemical action of rain and atmosphere; and to frost and vari ous mechanical forces, all tending to weaken it.
best building stones are those which have a compact formation, are not susceptible of chemical changes, and are easily worked. Granite comes nearest to perfection in this line. It is the strongest stone in use, and, having been employed for ages, is found to with stand severer tests than any other stone. It is a very hard silicious rock, having a massive and granular crystalline struc ture, containing the minerals quartz, feldspar, mica, horneblende, and, occa sionally, a little iron. The general color is gray, due to the presence of black mica or horneblende in the white quartz and feldspar. The red and pink varieties are caused by the presence of a red feldspar. The greatest granite beds in the United States are found in Maine and Massa chusetts. These granites are chiefly gray. A large amount of red granite is quarried in Nova Scotia, Scotland, and Sweden.
to granite, the most durable building stones are the lime stones. These vary greatly in both struc ture and color. One of the best varieties of this stone is the Indiana limestone. It has a white, or cream color, is of fine granular structure, and is readily worked. Many of the largest buildings in New York and Chicago are built of this stone. One of the best English building stones is the dolomite, or mag nesian limestone of the Permian forma tion, which ranges from Nottingham to Tynemouth. It is a double carbonate of lime and magnesia, containing a varying proportion of silica. The Houses of Par liament are built of this dolomite, which unfortunately decays rapidly under the influence of the London atmosphere.
is a purer grade of limestone, of a finely crystallized struc ture. It is composed almost entirely of calcium carbonate. Its color varies from
a pure white to a black, and it often oc curs with a red, yellow, or brown color. These colors are due to the presence of carbonaceous matter and iron oxides. Marbles occur in the United States in the beds of the Silurian limestone, which border the Appalachian Mountains, and also in the Rocky Mountains. The best grades are quarried in Vermont, and a very good marble for building use is found in western Massachusetts and in Connecticut. In Europe, the principal sources of marble are northern Italy, France, Spain, and Portugal. The Nu midian marble from Algeria has a great international reputation.
are composed of consolidated sand, and vary in color, structure, and composition. They are, as a rule, composed principally of quartz. The other substances they contain are chiefly carbonate of lime, alumina, and oxide of iron. In color, they vary from a gray, through buff and red, to brown; this coloration being due to the presence of iron as an oxide or carbonate. The sandstones mostly used in the United States are the Ohio freestones, or Berea grits, from the Subcarboniferous forma tion of Ohio, and the red and brown free stones of Triassic formation on the Atlantic coast. A blue-gray sandstone, containing a large amount of alumina, occurs in New York State, and, on ac count of its thin stratification, it is split in slabs and used for flagging purposes.
Serpentine.—This stone is composed of silica and magnesium in about equal por tions. It is a greenish color and of mas sive structure. It is rather soft, and is not very durable; but is used to a large extent in interiors and in the trimmings of churches and other places where a pleasing color effect is desired.
Trap.—Trap, or basalt, is one of the most durable stones known; but, on ac cot.nt of its extreme hardness, is little used in building. It is of igneous origin, and will withstand great changes in tem perature and extreme frost. It ranges from gray to black in color, is massive in structure, very heavy, and of irregular cleavage. It occurs in almost all parts of the world.
Besides these commoner stones, many others are employed for interior and or namental work, among them various col ored slates, onyx, alabaster, and a great variety of artificial stone, brick, and tile.
Government reports estimate the value of the best known building stones quar ried in the United States during 1918 as follows: