from the ore. These specular oxides of the azoic rocks of Missouri are proving immensely important, not only to the western states, but also to the general iron industry of the country. The demand for the ores is large, on account of their richness and purity, which render them suitable for admixture with magnetites, &c., of other localities, and adapt them especially for the manufacture of pig iron for use in the Bessemer process, and of wrought iron by the direct process.
IRON ORES. The term iron ore is limited to oxides of iron, either as such or in combination with water or carbonic acid. Other compounds of iron, as for example the sulphide, are not adapted for iron making. The term is further limited to deposits of sufficient purity and richness to render smelting profitable. These factors differ in different localities. Both the ferric and magnetic oxides occur in nature, sometimes nearly pure; they are called respectively hematite (red or anhydrous hematite) and magnetite. Ferric oxide also occurs in combination with water in various definite proportions; these compounds are called hydrous or brown hematites. Ferrous oxide is a component of many minerals, but only the ferrous carbonate is important as an ore of iron; it is known as spathic ore. Mineralogically iron ores may be grouped as follows:
| ORES. | Formula. | Crystalline form. | Hardness. | Specific gravity. |
Color of powder. | Per ct. metallic iron. |
Water. | Carbonic acid. |
| Ferric Oxide—Red hematite. | ||||||||
| Hematite | Fe₂O₂ | Hexagonal | 5.6-6.5 | 4.5-5.3 | Cherry red to reddish brown | 70.00 | . . . . | . . . . |
| Ferric Oxide Hydrated—Brown hematite. | ||||||||
| Limonite | Fe₂O₂,3H₂O | Massive | 5.5-5 | 3.6-4 | Yellowish brown to rusty yellow | 52.34 | 25.23 | . . . . |
| Xanthosiderite | Fe₂O₂,2H₂O | Massive or fibrous | 2.5 | . . . . | Ochre yellow | 57.14 | 18.37 | . . . . |
| Limonite | 2Fe₂O₂,3H₂O | Massive or earthy | 5-5.5 | 3.6-4 | Yellowish brown | 59.90 | 14.43 | . . . . |
| Göthite | FeO,CO₂ | Orthorhombic | 5-5.5 | 4-4.4 | Brownish to ochre yellow | 63.03 | 10.11 | . . . . |
| Turgite | Fe₂O₂,H₂O | Massive | 5-6 | 3.5-3.7 | Reddish | 66.28 | 5.33 | . . . . |
| Ferrous Carbonate—Spathic Ore. | ||||||||
| Siderite | 2Fe₂O₂,H₂O | Hexagonal | 3.5-4.5 | 3.7-3.9 | White | 48.27 | . . . . | 37.93 |
| Magnetic Oxide—Magnetite. | ||||||||
| Magnetite | Fe₂O₄ | Isometric | 5.5-6.5 | 4.9-5.2 | Black | 72.41 | . . . . | . . . . |
Iron ores rarely occur in masses of mineralogical purity. The hydrous hematites are so closely related in their formation, occurrence, and physical appearance, that their distinction is sometimes impossible without chemical analysis, but generally the groups are readily distinguishable. The color of the powder, or streak, is very characteristic. Turgite here forms an exception to the rule; but it is easily recognized on heating, since it decrepitates and gives off water. Nearly all the iron ores contain earthy substances. These are commonly silica, alumina, lime, magnesia, &c.; silica usually predominating. These substances are removed in the cinder on smelting. Manganese accompanies iron in nearly all its ores, but for the most part in small quantities; the spathic ores contain the largest proportion. Under favorable conditions the manganese is reduced in the furnace and unites with the iron; usually, however, the greater part goes into the cinder. Sulphur is found in many ores, either in the form of sulphuric acid or as iron pyrites. According to the conditions of the smelting, the sulphur may enter either the iron or the cinder. Phosphorus, in the form of phosphoric acid, is present in most iron ores, either combined with the oxide of iron, or mechanically disseminated as apatite (calcic phosphate). It is the most dreaded of all the impurities of iron ores, since no method has been discovered of eliminating it in the blast furnace; nearly the total amount of phosphorus in the ore goes into the iron. Titanium, as titanic acid, is present in many ores, especially magnetites. It renders the ores very difficult to smelt in the blast furnace; it is generally mainly removed in the cinder, but occasionally some of it unites with the pig iron. Chromium in small amount is not an unusual ingredient of iron ores; on smelting it probably passes mainly into the pig iron. Zinc is very commonly present in minute amounts; it is completely volatilized, and forms incrustations of white oxide around the furnaces. A brief description of the leading varieties of iron ore deposits, and their distribution, particularly in the United States, is all that will be attempted in this article.—1. Hematite. The term hematite (Gr. ἇιμα, blood) is properly applied to the sesquioxide only, since this has a red powder; but Theophrastus speaks of ἁιματίτης ξανθὴ, or yellow hematite probably an ochreous limonite. The ferric or sesquioxide occurs in several varieties. The specular ore has a crystalline structure, often forming beautiful splendent rhombohedral crystals. The famous mines on the island of Elba, worked before the beginning of the Christian era, furnish this variety in great purity. Sometimes the structure is foliated or micaceous, giving the ore a greasy appearance and feel; it is then called micaceous hematite. The more common varieties are the compact, columnar, and fibrous. It occurs also in concretions or botryoidal masses. Its color
