Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/303

IRON 287 more recent formations as a rule, but some considerable ones occur among the Coal Measures and Carboniferous Limestone ; the Oolite, Lias, Jurassic, Greensand, and "Wealden formations of England especially Northamptonshire and adjacent counties), and of France { Boulogne and the Ardeche), Luxembourg, Bavaria, and Wurtcmberg, contain deposits often of considerable magnitude and extent, which occasionally show distinct passage into red hsematite, and often pass age of clay ironstone into brown haematite. Bog and lake ores are considered by Ehrenberg to be mostly formed by infusorial agency ; on the dredging up of deposits of this kind (occurring in nodules and granular concretions), a new formation of lumps is often found to occur after the lapse of some years. In some cases these deposits are of large magnitude, e.g., those of Finland, Sweden, Norway, and Three Rivers (Canada). Pisolitic concretionary masses of a variety of brown hematite are found sometimes in largo quantity in the Ger man Oolites, and elsewhere in the cavities and crevices of limestones; these have been probably formed by deposition from water percolat ing through the rock, and the aggregation together of the ferric oxide thus thrown down, and the earthy matters also in suspen sion. The following table gives the composition of various kinds of ores belonging to the brown htematite class : Character ofi Ore and > Locality....) Morthamp- toushire Deposits. Pyrenean Ores used for the Catalan Forge. Pisolitic Ore, Audin- court, France. Limonite, Kentucky. London derry, Nova Scotia. Bog Iron Ore, Platen, Sweden. Analyst Spiller. Francois. Jordan. Caldwell. Chapman. Svanberff. Ferric oxide Manganese do.... 52-8G 0-51 7-39 65-50 3-00 1-30 70-00 trace 6-00 69-93 3-i2 83 1C 1-04 042 G7-59 1-45 4-18 7-4G 5-00 050 1-53 0-13 047 Magnesia 0-68 13-16 0-45 11-40 1005 1-62 13-45 0-15 4-12 0-23 7-81 Phosphoric ) anhydride) " Sulphuric do. ... Sulphur 1-26 6-03 0-24 0-29 002 0-18 Water 11-37 13-20 14-00 10-21 10-67 17 81 Carbonic > 4-92 anhydride) " 99-61 99-85 100-55 100-10 100-00 99-72 Total metallic^ iron j" 37-00 45-87 49-00 48-95 58-22 47-32 Magnetic Iron Ores. The substances most nearly approaching to the composition Fe :{ 4 sometimes occur well-crystallized in forms belonging to the cubic system, and possessing a semi-metallic lustre; in the mineral franklinite (found in large quantities in New Jersey) the ferrous oxide present is largely replaced by zinc and manganese oxides without altering the crystalline shape (usually octahedral). The purest magnetites are strongly magnetic, and often show polarity, then constituting loadstone; they differ from hrematites in the colour of the streak, magnetic ore yielding a black, red hcema- tite and specular iron a red, and brown hsematite a brown streak ; the specific gravity is about the same as that of compact red haema tite, viz., near to 5*0, while brown haematites are usually consider ably less dense, their specific gravity being near to 4 2. Massive deposits are found in the older formations in Sweden and Norway (crystalline limestones, talcose schists, and diorites), North America (Laurentian series), the Ural mountains (doleritic porphyry), and Mexico (Cerro Mercado felspathic porphyry) ; whilst considerable amounts are also found in somewhat more recent formations, e.g. , in Piedmont (Traversella talcose schists and dolomites), Spain, northern India, and Saxony (Berggieshiibel); in England only com paratively small quantitiesare found, notably at Rosed ale (Yorkshire) and Brent and Dartmoor (Devonshire). The mines of Dannemora (southern Sweden) and Gellivara (Swedish Lapland) are of great antiquity, the iron produced from the ore thence raised being of the finest quality (partly owing to the use of charcoal in smelting); the Indian mines have also been a source of wootz for some two thousand years at least, whilst the Traversella deposits have been worked from time immemorial. Notable amounts of magnetic ore also occur in various parts of France, Germany, Spain, Portugal, North Africa, Greece, Australia, and Brazil; whilst in New Zealand (Taranaki), as also in the Bay of Naples, and especially along the north-east coast of British America and Labrador, enormous quan tities of " iron sand " occur along the beach, derived from the dis integration of rocks containing crystalline magnetic oxide of iron (usually more or less titaniferons) ; this variety of magnetic oxide is capable of resisting indefinitely the oxidizing effect of air and water, and from its hardness and density becomes mechanically separated from the felspathic and silicious particles of matrix simultaneously formed during the erosion of the rocks ; owing to its great freedom from sulphur and phosphorus, it is practicable to obtain from it (by the aid of charcoal) the finest qualities of iron. It has been sup posed by some that the presence of titanium in the ore communi cates special qualities to the steel thence prepared ; but evidence in proof of this is requisite, inasmuch as it seems that the titanium present in the pig iron smelted from titanifcrous ores, to the extent of some tenths per cent, or more, becomes eliminated during the transformation into malleable iron and steel just as silicon is similarly oxidized and removed. The following analyses illustrate the composition of various kinds of magnetic ore : Character of ( Ore and < Locality .... ( Rose- dale, York shire. Dannc- moia, Sweden. Magnetic von Sand, Moisie River, St Lawrence, Canada. Titani- fcrous Iron Ore, Chug Valley, Wyoming. New Jersey Mag netite. Luke Champlain Ore, Moriah, " No. 21 " Bed. Analyst Pattin- Ward. Stony Bertolet son. Hunt. Ferric oxide Ferrous ,, Manganese oxide Alumina 32-67 33-85 0-09 3 15 27-55 ) 58-93 ) o-io 0-29 92-60 | 0-40 45-03 1796 1-53 3-98 G3-18 ) 26-52 f 0-12 3. 28 95-99 0-10 2 00 Lime 2-86 C 38 090 I ll 8 Magnesia 1-59 6 1 1-56 O GO Silica 7-79 12-54 1-95 76 C-C8 (.-,,1 Phosphoric ) anhydride j" " Sulphuric do Carbonic do Sulphur 1-41 trace 1036 003 trace 6-12 "0-04 trace 1 44 0-054 O-Ol 9 0-10 O lO Water . 376 Oil Titanic oxide 4-15 3-49 Chromium do. . 2-45 Zinc do 047 98-1G 10067 10000 99-78 100-226 100-05 Totai metallic ) iron ) 40-17 G2C GG-73 45-49 64-86 9-51 Sjiathose Iron Ores. Ferrous carbonate, being isomorphous with magnesium, manganese, and calcium carbonates, frequently occurs crystallized either by itself as sidcrite or with large intermixture of one or the other of these salts ; when manganese is present to any considerable extent, the ores are more especially suitable for the production of spiegeleisen and ferro-manganese, especially when they contain little or no phosphorus. In Great Britain the chief deposits are those of Weardale (Carboniferous Limestone), Alston Moor (Cumberland), Brendon hills (Somerset), andExmoor (Devon shire) ; these frequently show passage of the mineral into brown haematite by oxidation through access of air and moisture. Large massive deposits are found in Germany (Stahlberg near Miisen, Westphalia), Styria (Eisenerz), Thuringia, and Carinthia, mostly in rocks of the Devonian period or thereabouts, and sometimes consti tuting almost entire mountains ; also in the Basque provinces, the Pyrenees, South Spain, and Nova Scotia. These ores are as a rule extremely free from phosphorus and sulphur, whence they are largely employed for the manufacture of malleable iron, steel, and spiegeleisen of high qualities; they are of notably less density than compact hajniatite or magnetite, usually possessing a specific gravity of near 3 8. The following analyses represent the com position of certain kinds of spathose ore : Wear- Brendon Hills, Eiscnerz, Miisen, West Allevard, Isere, Pictou County, dale. Somer setshire. Styria. phalia. France. Scotia. Tookey. Spillcr. Peters. Jordan. Thorpe. Ferric oxide Ferrous ,, 0-81 49-77 O Sl 4384 53 : 42 2-75 48-5T 48 : 15 54-99 Manganese oxide ... 1-93 12-64 0-01 3-08 0-83 163 3-02 2-85 3-96 0-28 1-75 2-50 1-53 2-83 3-03 5-00 2-29 0-57 0-55 Silica 3-12 0-07 0-06 1-62 4-85 2-70 Phosphoric ) anhydride j" Carbonic do Water trace 37-20 0-30 S8-86 O lS 38-10 0-54 39-92 0-45 nil 40-49 33-60 0-04 Sulphur 0-04 0-22 0-16 3-48 99-96 100-32 99-66 100-55 99-73 99-70 Total metallic iron 38-95 ! 34-67 41-51 42-59 37-45 42-76 Clay Ironstone. When ferrous carbonate occurs largely mixed with clayey matter, the crystalline structure is usually non-apparent; frequently so much calcium carbonate is also present as to make the ores useless for smelting purposes except when intermixed with others, the calcareous matter then serving as flux ; nodules of this poor or " lean" ironstone found in the London clay and elsewhere are, however, largely used in the manufacture of cements, and hence are often known as cement stones. The largest deposits of clay iron stone are found in the Coal Measures, and often exhibit distinct stratification, fossils being not unfrequently met with, especially in the nodular varieties ; llackband ores (layers of ironstone and clay alternating with coaly matter) are largely found in Staffordshire, Wales, and Scotland, and to some extent in the Rhenish and West-