ABRASIVES, or those substances used in grinding or polishing, include (1) mineral sub stances, such as grindstones, millstones and whetstones, which are used by simply shaping up the material found in nature; (2) mineral substances which occur disseminated in the rocks or which must first be freed from im purities and are prepared for use by an initial granulation; (3) artificial abradants. The his tory of abrasives shows that in ancient times the first class was used, the artificial abrasives now so extensively employed being unknown until quite recently.
Grindstones are manufactured from a tough, gritty sandstone, found chiefly in Ohio, though Michigan, Colorado and West Virginia add to the output, and England, Scotland and Bavaria are also producers. The Ohio and Michigan stones are quarried from the Berea grit (q.v.) of Mississippian age. The production of grind stones in the United States in 1915 amounted to Millstones and Buhrstones are far now than before the introduction of the roller process of making flour, for while the American production in 1880 amounted to 000 it fell in 1894 to $13,887. Since 1894 it has steadily increased till in 1912 it was $71,414. The 1915 output was valued at $53,480. This is owing to the increased demand for buhr stones for grinding the coarser cereals, fertiliz ers, cement rock and various minerals. Mill stones are finer grained and more compact than grindstones. They are usually made from sand stone or a quartz conglomerate. The buhrstone (q.v.) from France is the best, but the stones from New York and Virginia meet most of the requirements of the trade. A few are made in Pennsylvania and North Carolina. There are buhrstone deposits in Vermont, Ohio and Ala bama which have not been worked of late years; also a newly discovered deposit in Cali fornia of stone equal to the French. The New York stones come from the Shawangunk grit of Silurian age.
Oilstones, Whetstones and Scythestones are to a large extent American products. For nearly a century New Hampshire was the head quarters of the whetstone industry, but Ar kansas has held the lead for some years. Whet stone rock is also found in Vermont, Ohio, Kentucky, Pennsylvania and Indiana. The best oilstones from New Hampshire are inferior to those of Garland County, Ark., in which region there are extensive beds of a remarkably compact, white, Paleozoic quartz rock, called Novaculite. Griswold in 1890 announced that this material is a sedimentary deposit of fine grained quartz and not a chemically precipitated deposit as had been previously supposed. The quarries were largely worked for implements in prehistoric times and since 1840 they have yielded the finest oilstones known. These are sold under the names of ((Washita" and oilstones. The production of oil stones and whetstones in the United States dur ing 1915 amounted to $115,175. The imports, chiefly of razor hones from Belgium and Ger many, and of "Turkey" oilstones from Italy and France amounted to $14,247 — about one third the normal value. Ohio leads in the pro duction of scythestones, New Hampshire, Ver mont and Michigan contributing important shares.
Pumice (q.v.), a spongy lava, or a volcanic ash, is used in scouring powders and soaps. It comes chiefly from the Lipari Islands, but is also produced in Utah and Nebraska. The pro duction of the United States in 1915 was valued at $63,185; the imported pumice at $65,691. Infusorial or diatomaceous earth (Kieselguhr) occurs in beds often miles in extent. It is formed of the siliceous shells of infusoria and diatoms, and is used in scouring soaps and polishing powders. The chief American lo calities are in Maryland, Virginia, New Hamp shire and California. The United States pro duction for 1915 was 4,593 tons, valued at $38,517; but these figures cover not only that used as abrasive, but also a much larger quan tity used by sugar refiners and to insulate boilers, etc. Tripoli is a similar variety of opal, but formed from a siliceous limestone by the leaching out of the calcium carbonate. Its use
as an abrasive is as a polishing powder for metals, etc., but it is also extensively manu factured into filters, for which it is admirably adapted. Extensive deposits are worked at Seneca, Mo., and in Illinois, but the chief supply is imported from Tripoli. The United States production for 1915 was 30,711 tons, valued at $572,504— four times the output in 1911. The 1915 importation of tripoli was valued at $27,333. Crystalline quartz, of which 112,575 tons were mined in Connecticut and Pennsylvania in 1915, is used as a wood finisher, in the manufacture of sandpaper, in the sawing of marble, for cleaning castings, etc. Garnet (q.v.) occurs in many of the crystalline rocks, especially in pegmatite and mica schist. Many varieties are recognized by the mineralo gist; but the value of garnet as an abrasive, aside from its great hardness, is dependent not on its composition, but on its structure. If this is distinctly lamellar the material will con tinually present the sharp edges which are so essential to a good abrasive. Garnet which lacks this lamellar structure is of comparatively little efficiency for grinding and smoothing. Garnet is of little value for grinding metals but is of great utility in woodworking. Its low melting point prevents its bonding with refrac tory materials. Garnet-paper is much superior to sandpaper and is extensively used in wood working and finishing the soles and heels of shoes. The most important localities are in New York and New Hampshire. The output for 1915 amounted to 4,301 tons, valued at $139,584. Corundum (q.v.), being the hardest mineral known, except the diamond, ranks next to it among the natural abrasives. It occurs in enormous quantities in Ontario, which since 1901 has been the leading producer. It was at one time extensively mined in Montana, North Carolina and Georgia which furnished nearly all of the domestic supply, but since 1906 no corundum has been produced in the United States. Small quantities of corundum are pro duced in India which go chiefly to the English market. The chief deposits of corundum are of magmatic segregation origin, having solidified from a fluid state during the crystalli zation of very basic igneous rocks. The value of any sample of corundum depends largely upon its fracture, the crystals which break smooth being of very limited use. Emery (q.v.) is a natural mixture of corundum with magnetite or hematite. It has been largely mined at Chester, Mass., and Peekskill, N. Y., but the Massachusetts mines have not been operated of late years. The chief supply, however, comes from the Island of Naxos, Greece, and from Asia Minor. The material is brought to this country as ballast and owing to the low prices at which it is marketed, the sale for the American mineral is much reduced. The United States production for 1915 was 3,063 tons valued at $31,131 — five times the usual output. The Canadian output of corun dum in 1915 was $37,798— about one-sixth the usual production. The importation of emery and corundum was valued at $271,649 — about 55 per cent of the average. Diamond (q.v.), owing to its far greater hardness, brings many times the price per carat which any other abrasive brings per pound. The black amor phous found in Brazil is much harder than the crystallized diamond, but it is almost exclusively used for diamond drills, while the dust of the South African abort' is the material commonly employed as an abrasive in the cutting of diamonds and other precious stones. In 1915 the importation was valued at $75,944. A large division of natural grinding material in the form of quartz pebbles may properly be included under abrasives. For merly imported altogether, from Denmark, France, Sweden, Labrador and Newfoundland, the war cut off the supply and led to a develop ment of American deposits, chiefly in Nevada, though in many instances hardened steel balls have been found an effective substitute.