Limonite

“ In such cases we have fibrous, oolitic or compact masses, according to the form in which the limonite occurred. The transformation from limonite into hematite involves some heat to drive out the water of crystallization, but nothing like what is involved in metamorphism.
Hematite is the source of 90% of the iron mined in this country. Part of it comes from the famous Clinton iron ore, a layer a foot or more in thickness; starting in New York State, and extending all down the Appalachian Mountains to Alabama, where it is ten or more feet thick and the basis of the Birmingham iron industries. ”

“ An oolitic structure is sometimes present, and the ores are generally phosphatic, and may contain perhaps 30% of iron. The oolitic brown ores of Lorraine and Luxemburg are known as “minette,” a diminutive of the French mine (ore) , in allusion to their low content of metal. Granular and concretionary limonite accumulates by organic action on the floor of certain lakes in Sweden, forming the curious “lake ore.” Larger concretions formed under other conditions are known as “bean ore.” Limonite often forms a cementing medium in ferruginous sands and gravels, forming “pan” ”

“ From the standardization data already obtained, and the known weight of the sample, calculate the percentage of iron (Fe) in the limonite.
[Note 1: Limonite is selected as a representative of iron ores in general. It is a native, hydrated oxide of iron. It frequently occurs in or near peat beds and contains more or less organic matter which, if brought into solution, would be acted upon by the potassium bichromate. This organic matter is destroyed by roasting. Since a high temperature tends to lessen the solubility of ferric oxide, the heat should not be raised above low redness.] ”

“ In shallows, and especially in lakes, where soluble salts of iron become readily oxidised, brown iron rust, the mineral limonite, is continually forming at the surface and sinking to the bottom, where it firmly cements the sand. ”

“ Limonite is a very common mineral, the color, streak and hardness identifying it readily. Iron rust is its most familiar form. When powdered it is the ochre yellow used in paints. Being so universally distributed, it is to be expected it will occur in a variety of ways. First, there is the fibrous type found lining cavities, in geodes, or hanging in stalactites in caves. This has a silky luster, an opalescent, glazed or black surface, and is in mammillated or botryoidal masses. ”

“ Commercial deposits of limonite occur in southeastern Missouri where large boulders, discontinuous and irregular lenses or beds, pipes, nodules, and gravel to clay-sized particles of the mineral are associated with the cherty, gravelly residual clay. Usually the ore is crushed, hand-sorted, and washed preparatory to concentration for shipment to a furnace or for use in cement manufacture. As in the case of hematite, unless one has a deposit amounting to thousands of tons of ore it has little commercial value, and unless the mineral is relatively pure it can not be used. ”

“ It is not with the ordinary products of contact or general metamorphism that we have here to deal; but with the remarkable surface-collections of silicified corals, nodules and flints of chalcedony, fragments of white quartz-rock, bits of jasper, and certain curious siliceous concretions, that occur often in association with fragments of limonite in these low-lying regions. ”

“ This well-marked hill, situated at the extreme northerly end of the depression, consists of a mass of ferruginous material, including limonite, pisolitic iron-ore, red and yellow ochre, etc., lying on a series of sandy shales, clays and sandstones belonging to the Cenomanian (Series No. 7) . Thin bands of limonite, etc., occur in the clays and sandstones, but the great mass of mineral appears to form a distinct deposit capping, and in part replacing, the former. The iron-ore occurs in every stage of purity. ”

“ LIMONITE, or Brown Iron Ore, a natural ferric hydrate named from the Gr. λειμών (meadow) , in allusion to its occurrence as “bog-ore” in meadows and marshes. It is never crystallized, but may have a fibrous or microcrystalline structure, and commonly occurs in concretionary forms or in compact and earthy masses; sometimes mammillated, botryoidal, reniform or stalactitic. The colour presents various shades of brown and yellow, and the streak is always brownish, a character which distinguishes it from haematite with a red, or from magnetite with a black streak. ”

“ The Limonite is seldom found pure, and its deposits are so scarce, that they can with difficulty be profitably used for the extraction of iron; nevertheless, mixed with carbonate of lime, it is rather frequently found in each of the three preceding kinds of rocks, especially in the limestones and marls. ”

“ Kaolinite is white to yellow, and limonite or ochre is yellow to orange. Limonite also appears in orange-colored or brown balls, in icicle-like masses, and in thin beds. Specimens have approximately the hardness of a knife. Quartz does not decay easily and remains behind in solid granules.
The Minerals of Sedimentary Rocks
Most sedimentary rocks are formed by the cementation of deposits of transported waste, derived from older materials. ”

“ Nodules of pyrites and of marcasite are common in many clays, sandstones and marls. Their outer surfaces are tuberculate; internally they commonly have a radiate fibrous structure. Usually they are covered with a dark brown crust of limonite produced by weathering; occasionally imperfect crystalline faces may bound them. ”

“ The beautiful resinous or pitchstone-like rock from near Airthrey Castle has been found by Mr. Watts to be a glassy hypersthene-augite-andesite, since among its phenocrysts of plagioclase, augite and hypersthene both occur. Magnetite is commonly traceable, and apatite may be occasionally detected. As the result of decomposition, calcite, chlorite and limonite are very generally diffused through the rocks. ”

“ Like hematite this mineral belongs to the hexagonal system, and crystallizes in hemihedral form, making the rhombohedron. Its faces are often curved, which is rare in minerals, only a few forms like this and dolomite having other than plane faces. When siderite crystals grow in clusters, the crowding often results in growth on one face only, making a mass of fibrous character, and in such cases the surface of the mass is botryoidal in contour. The mineral is likely to oxidize, losing its gray-brown color, and becoming limonite. ”

“ In metasomatism, on the other hand, chemical alteration is supposed by most geologists to be an essential feature; new minerals appear, but the original structures are sometimes retained.
The facility with which a rock undergoes metasomatism depends partly on its nature, and partly on the circumstances in which it is placed. Limestones, being readily soluble under natural conditions, are especially liable. The Cleveland iron ores of Yorkshire are limestones replaced by siderite and limonite; the Whitehaven iron ores are metasomatic replacements of limestone by haematite. ”

“ Pure limestone is white, but if it contains clay or plant or animal matter it is light gray, dark gray, or black. Limestone also may be some shade of yellow, brown, or red. It is fairly soft and can be scratched with a knife. Because this rock contains calcite, an easy chemical test will help identify it: a drop or two of dilute hydrochloric acid will quickly fizz and bubble when placed on the limestone.
Limestones form in fresh water, such as in lakes, but most of them form in the seas. As some earlier-formed rocks are weathered, the calcium minerals that they contain are dissolved. ”

“ When therefore a magnesian limestone is burnt, the magnesia is deprived of its carbonic acid much sooner than the lime, and in this state it is a poison to plants. That more magnesian lime may be used upon rich soils, [111] 408 seems to be owing to the circumstance, that the decomposition of the manure in them supplies carbonic acid, and thus converts it into a mild carbonate. Besides being used in the forms of lime and carbonate of lime, calcareous matter is applied for the purposes of agriculture in other combinations. The principal body of this kind is gypsum, or sulphate of lime ”

“ Citric or acetic acid will effect this change, though the mineral acids are more commonly employed. Limestones, when pure, are soft rocks readily scratched with a knife-blade or the edge of a coin, their hardness being 3; but unless they are earthy or incoherent, like chalk or sinter, they do not disintegrate by pressure with the fingers and cannot be scratched with the finger nail. When free from impurities limestones are white, but they generally contain small quantities of other minerals than calcite which affect their colour. ”

“ Combined with carbonic acid (26) it forms limestone (140) , chalk, and marble; all of which are capable of being converted into lime by burning. Lime may also be obtained from oyster and other sea shells. When pure, it is of white colour, and moderately hard substance, though it is easily reducible to powder. Its taste is burning and acrid; and, like the alkalies, it changes vegetable blue colours to green. It has likewise the property of corroding and destroying animal substances. Lime, when pure, absorbs water rapidly, becomes hot, and falls into powder. ”

“ If every farm could get its supply of pure calcium lime as cheaply as it can have magnesian lime, the truth respecting the value of the latter would have small agricultural importance, but as a great bulk of farm and commercial supplies of lime is magnesian, financial injury has been done consumers who have paid more than should have been paid for relatively pure calcium lime and limestone, being afraid to use goods whose content of magnesium was not small. ”

“ Limestone and chalk are usually rich in lime and phosphates, but deficient in humus, silica, sulphur, and alkalies. Sandy soils are rich in silica, but are generally poor in respect of phosphates and alkalies. Therefore, on a clay or loam, farmyard manure is invaluable, because it contains ingredients that all crops appreciate, and also because it is helpful in breaking up the texture of the soil. The occasional application of lime also is important for its almost magical effect on garden soil that has been liberally manured and heavily cropped for a long term of years. ”

“ When it has absorbed carbonic acid, and become reconverted into carbonate, the original caustic lime has no chemical virtue over chalk, rich shell-sand or marl, or crushed limestone. It has, however, the important mechanical advantage of being in the form of a far finer powder, than any to which we could reduce the limestone by [Pg 197] art—in consequence of which it can be more uniformly diffused through the soil, and placed within the reach of every root, and of almost every particle, of vegetable matter that is undergoing decay. ”

“ Of all known substances, lime, in the form of lime-water, acts most energetically in producing this change; but other solutions of lime, as well as most salts and mineral acids, produce the same effects when used in sufficient quantity. Common salt is among the most convenient, because it can most readily be leached out of the clay precipitate thus thrown down. This when white, resembles boiled starch, but being usually colored by iron might be easily mistaken for the mixed precipitate of ferric hydrate and alumina so commonly obtained by chemists in soil analysis. ”

“ Davy, therefore, very properly introduces the subject, by a description of the nature and qualities of these bodies, and by marking the distinctions between quicklime and its carbonate.
The substance commonly known by the name of Limestone is a compound of lime and carbonic acid, associated generally with other earthy bodies, the nature and proportions of which vary in different species. "When a limestone does not copiously effervesce in acids, and is sufficiently hard to scratch glass, it contains siliceous, and probably aluminous earth. ”

“ Limestone consists principally of crystalline particles of the mineral calcite (fig. 1) . This mineral is glassy in appearance and is composed of calcium, carbon, and oxygen combined to form calcium carbonate—CaCO3. Dolomite is largely made of crystalline particles of the mineral dolomite, which also has a glassy appearance and consists of calcium, magnesium, carbon, and oxygen—CaMg (CO3) 2. The crystalline particles of limestone and dolomite vary in size. Some are coarse enough to be seen easily, others are so small that they can be distinguished only with a microscope. ”

“ Ours is the natural country of the lime, lemon and citron; children of a common stock. We have several varieties of the lime. The trees are of rapid growth, constant bearers, very prolific, subject to no disease, and very tenacious of life. The fruit is large, “How large?” as a Sicily lemon. I consider the lime as profitable as the orange, and more so, with us. It should be cultivated for citric acid, of which it yields more than any other fruit. The time will come when our part of Florida will supply citric acid to the world. A peck of limes will yield a gallon of juice ”

“ One of the reasons for applying ground limestone to soils which are deficient in lime is to furnish the element calcium in suitable form for the formation of nitrates in the process of nitrification. Ground limestone is calcium carbonate (CaCO3) , a compound containing one atom of calcium (Ca) , one atom of carbon (C) and three atoms of oxygen (O3) . This is the same form of lime which is contained naturally in limestone soils—soils which are noted for their great productiveness—and it is generally the most economical form of lime to use for correcting soil acidity and promoting nitrification. ”