Page:The American Cyclopædia (1879) Volume IX.djvu/421

Rh is brownish red to iron black (red hematite). Occasionally it is earthy in character (red ochre). An argillaceous variety is known as clay ironstone, or argillaceous hematite. It is also often oölitic in character. All the varieties have the red streak in common. Hematite is found with the iron partially replaced by titanium, giving rise to various mineral species, such as menacannite and ilmenite. They have the general formula (Ti, Fe, Mn, Mg)₂O₂, and contain from 3.5 to 59 per cent. of titanic acid. The hematite ores are as a rule of great purity, and from them is made a large proportion of the finer varieties of iron and steel. Nearly all the Bessemer pig iron in England and America is made from red hematite. “It occurs in rocks of all ages. The specular variety is mostly confined to crystalline or metamorphic rocks, but is also a result of igneous action about some volcanoes, as at Vesuvius. Many of the geological formations contain the argillaceous variety or clay ironstone, which is mostly a marsh formation, or the deposit over the bottom of shallow, stagnant water; but this kind of clay ironstone (that giving a red powder) is less common than the corresponding variety of limonite or siderite. The beds that occur in metamorphic rocks are sometimes of very great thickness, and, like those of magnetite in the same situation, have resulted from the alteration of stratified beds of ore, originally of marsh origin, which were formed at the same time with the enclosing rocks, and underwent metamorphism, or a change to the crystalline condition, at the same time.” (Dana.) The hematite ores are widely distributed. Immense beds occur in Chili, and it is said in other South American states. The mines of Norway, Sweden, Lorraine, Switzerland, Saxony, Bohemia, and the Hartz also contain this ore. Unusually pure varieties are found in the mountain limestone of the carboniferous system in Cumberland and North Lancashire, England; and remarkably fine fibrous hematite is mined in Wales. At Bona, Algeria, there are extensive deposits of pure hematite, which is exported to France, England, and the United States for the manufacture of Bessemer steel. In the United States there are immense deposits of specular ore in the azoic rocks of the Marquette region, south of Lake Superior. These deposits probably consist chiefly of martite, which is sesquioxide of iron crystallizing in isometric forms, and supposed to be pseudomorphous after magnetite. According to this hypothesis, the Marquette ore beds were once all magnetite in composition, and have been changed to sesquioxide by the addition of oxygen. Some of these deposits present masses of absolutely pure ferric oxide; the majority, however, are more or less silicious, containing streaks and masses of jasper. The amount of sulphur and phosphorus is small, and the ores are consequently well adapted for the manufacture of steel. They furnish a large proportion of the Bessemer pig iron of the

United States. Missouri, which is one of the richest states in iron ores on the North American continent, contains specular ore in porphyry and in sandstone, as well as in disturbed and drifted deposits, and also strata and drifted deposits of compact and earthy red hematites, supposed to be in many cases the product of an alteration of the specular ores. The most famous deposits are those of Iron mountain and Pilot Knob. At Iron mountain, which is the largest ore deposit in Missouri, a hill of decomposed porphyry 250 ft. high is traversed by numerous ore seams, and cut in two by an enormous vein of specular ore from 40 to 60 ft. thick, besides being covered with surface ore in rounded bowlders and fragments of variable size, in a stratum usually from 1 to 5 ft. thick. At Pilot Knob the ore is not in veins, but forms a regular bed in the porphyry of blue conglomerate. Shepherd mountain, Cedar hill, and other localities show similar deposits. The Missouri specular deposits in sandstone belong to the lower Silurian formation, and seem to have been originally formed in lenticular shape. The red hematites of the carboniferous formation of Missouri extend over large areas, as beds impregnating or replacing the ferruginous sandstone. All the Missouri specular iron is more or less magnetic, and in some cases it possesses polarity. Specular ores and massive or earthy and oölitic red hematites occur in the great azoic region of northern New York, in St. Lawrence, Clinton, and other counties. The Sterling, Parish, and other mines are famous. The Rossie hematites are now brought in considerable quantity to the Hudson river, for smelting with the magnetites of Lake Champlain. It is said that these hematites are so nearly pure as to permit the use of a considerable portion of them in the manufacture of Bessemer pig. In North and South Carolina a micaceous ferric oxide in schistose rocks, called itabiryte or specular schist, occurs. It is found also in great beds in Canada. In some parts it is a rich ore of iron, and in others passes into ordinary chloritic schists. The Laurentian system in Canada contains beds of hematites, or oligist iron ore, in large irregular masses, as on Lake Nipissing, arranged in the planes of stratification. Similar ore occurs in small beds in the Potsdam sandstone. Specular ores occur in Maryland, Virginia, and other southern states, but do not yet constitute so important a source of iron production as the brown hematites, magnetites, and argillaceous carbonates. Maine and New Hampshire also present red hematite deposits, the largest of which is on the Aroostook river in the former state. The finest iron ore of this variety yet discovered west of the Missouri river is the deposit of red hematite near Rawlins, Wyoming territory. It is massive and very pure, and has been mined to a considerable extent and shipped to Salt Lake, where it has been charged in the lead-smelting furnaces, as a flux for the production of