Page:The American Cyclopædia (1879) Volume IX.djvu/422

408 an iron slag.—2. Hydrous or Brown Hematite (brown ore, bog ore, ochre, lake ore, marsh ore). The brown hematites belong to the most recent iron formations, and occur in great abundance. They constitute a series, in which the physical characters vary as the proportion of water diminishes, passing from earthy varieties having a yellowish streak to compact masses, with brown streak inclining to red. Turgite, which has the lowest amount of water, and is therefore nearest to red hematite, has already a red streak. The usual condition of hydration is that of limonite, which may be regarded as the typical brown hematite. The other varieties enumerated are exceptional. This ore occurs in a great variety of conditions, as earthy or ochreous masses, or in concretionary, stalactitic, or hard, compact, mammillary, and botryoidal aggregations. It has often a distinct fossiliferous character, and is associated with vegetable and animal remains. All the varieties yield water when heated, and all except turgite give a yellowish or brownish streak. Brown hematites differ widely as regards purity. Usually they contain considerable silica and phosphoric and sometimes sulphuric acid, and are consequently rarely employed exclusively for the finer varieties of iron and steel. They however supply a large proportion of the iron that is used for castings. “Limonite occurs in secondary or more recent deposits, in beds associated at times with barite, siderite, calcite, aragonite, and quartz, and often with ores of manganese; also as a modern marsh deposit. It is in all cases a result of the alteration of other ores, through exposure to moisture, air, and carbonic or organic acids, and is derived largely from the change of pyrite, siderite, magnetite, and various mineral species (such as mica, hornblende, and augite), which contain iron in the protoxide state. It consequently occupies, as a bog ore, marshy places over most countries of the globe, into which it has been borne by streamlets from the hills around; and in the more compact form it occurs in stalactites as well as in tuberose and other concretionary forms, frequently making beds in the rocks which contain the minerals that have been altered into it. In moist places, where a sluggish streamlet flows into a marsh or pool, a rust-yellow or brownish yellow deposit often covers the bottom, and an iridescent film the surface of the water; the deposit is a growing bed of bog ore. The iron is transported in solution as a protoxide carbonate in carbonated waters, a sulphate, or as a salt of an organic acid. The limonite beds of the Green mountain region were shown by Percival to be altered beds of pyritiferous micaceous and argillaceous schist; and the same is held by Lesley as true also of the other beds of the Atlantic border, from New England and New York, through Pennsylvania (Mt. Alto region and others), to Tennessee and Alabama.” (Dana.) Brown hematite is the most universally diffused of all the ores of iron, and furnishes a large proportion of the iron of the world. In the United States it is distributed very widely and abundantly. Large deposits occur in New England, particularly in the neighborhood of Salisbury and Kent, Conn., and in Columbia and Dutchess counties, N. Y. The ores of these deposits are highly prized. Similar deposits of limonite are traced in a zone extending from the Hudson river to Alabama, along the line of the north flank of the South mountain, Blue Ridge, and Smoky mountain range, and also in the lower Silurian limestone valleys of Pennsylvania and Virginia, Nittany valley, Kishicoquilis, &c.; and again, under similar geological conditions, in East Tennessee, where the deposits near Embreeville are estimated by Lesley, Maynard, and others to contain many millions of tons of excellent ore. Western North Carolina and northwestern Georgia contain portions of the same zone, which ends in the magnificent deposits of Alabama. The siderite clay ironstones of the carboniferous and other rocks frequently furnish by oxidation deposits of brown hematite. This is the case particularly near the outcrop, but sometimes also throughout large deposits. The lignites of New Mexico, Colorado, and Montana are accompanied by ores of this character. The same is the case in the Appalachian region, for instance at Brady's Bend, Pennsylvania, in West Virginia, and elsewhere, and among the carboniferous iron ore deposits of Ohio, Indiana, Kentucky, &c. Large deposits of limonite occur in dolomite, associated with zinc ores, in Arkansas. Texas is also abundantly supplied with this ore. Brown hematite (bog ore and ochre) is found in large quantities in Canada, particularly in the St. Lawrence valley, where it overlies superficial deposits of clay and sand. The distribution of brown iron ores in other countries is so nearly universal that the localities need not be named. It may be remarked that the extensive deposits of Styria and Carinthia in Austria, and of Nassau on the Rhine, are celebrated for their purity and freedom from phosphorus—an element which, by reason of the usual organic origin of such deposits, is most likely to be found in them. The universality of this ore naturally follows from the fact that it is the ultimate result of the chemical metamorphosis of all other kinds of iron ore; so that wherever any ore of iron is exposed to oxidizing agencies and moisture, some form of limonite or hydrated ferric oxide of iron is certain to occur. The term limonite is derived from the Greek, moist grassy land, and refers to that variety which is known as bog ore or marsh ore. Famous ochreous deposits occur at Brandon, Vt. At Pointe du Lac and St. Ann, Montmorenci, Canada, are remarkable localities of the ochre, and at the latter place it is seen in the process of formation. The deposit varies from 4 to 17 ft. in thickness, and covers an area of four -