The most famous marble known to the ancients was the Parian marble, which was a finely granu lar and very durable stone, of waxy appearance when polished. Some of the finest Grecian sculp tures were formed of this marble, among them being the Venus de' Medici. The Pentellic marble was at one time preferred by the Greeks to Parian, because it was whiter and finer grained. The Parthenon was entirely built of it. It does not resist the weather well. The quarries at Carrara were known to the ancients, hut their chief importance has been in modern times. The temple of Jupiter Sera pie near Naples was constructed of a gray streaked micaceous marble, much used by the ancients and known as cipo Marble suitable for structural work sells at from $1.50 to $4 per cubic foot, while statuary marble brings $12 or $15 per cubic foot. Marble must commonly meet certain requirements as to strength, color, texture, freedom from flaws, and durability in the open air. Its crushing strength is commonly from 10,000 to 12,000 pounds per square inch.
The opening of a marble quarry is usually expensive and attended with financial risks, as a thickness of from 10 to 30 feet of rock usually has to be taken before sound marble is reached. After a sufficient area of surface has been pre pared by the removal of the imperfect stone, channeling machines, which may be either per ettsiion or diamond drills, are set to work, and rectangularly crossed channels are cut to a, desired depth, say from 5 to 7 feet. One of the
blocks, called the key block, is then broken off at the base by wedging and lifted out with a crane. This gives ready access to the others, which are then drilled as circumstances may require, the quarry being worked out in floors. The blocks removed commonly run 4 feet 6 inches by 6 feet 6 inches, but much larger ones are sometimes extracted on special demand. The marble after quarrying is taken to the mill and sawed into blocks or slabs, or chiseled into mon umental pieces. The first smoothing is done with sand and water, but the final polishing with a mixture of putty powder and weak acid rubbed on with a flannel-covered revolving buffer. The total value of marble produced annually in the United States exceeds $4,000.000.
BIBLIOGRAPHY. Merrill, Stones for Building Bibliography. Merrill, Stones for Building and Decoration id.. ":11ineral Resourees," United States Geological Surrey (Washington. annual) ; MeCallie, "Marbles of Georgia," in Georgia Geo logical Surrey : Hopkins. "Report on Marbles." .1 rkansas Geological Surrey. vol. iv. (1S90) ; Ries, "Limestones and Marbles of Western Now England," Seventeenth Animal Report United Slates Geological Survey (Washington, 1896); :gone (New York, monthly). See BUILDING STONE.%