LIMONITE, or

See also:

• BROWN
• BROWN, CHARLES BROCKDEN (1771-181o)
• BROWN, FORD MADOX (1821-1893)
• BROWN, FRANCIS (1849- )
• BROWN, GEORGE (1818-188o)
• BROWN, HENRY KIRKE (1814-1886)
• BROWN, JACOB (1775–1828)
• BROWN, JOHN (1715–1766)
• BROWN, JOHN (1722-1787)
• BROWN, JOHN (1735–1788)
• BROWN, JOHN (1784–1858)
• BROWN, JOHN (1800-1859)
• BROWN, JOHN (1810—1882)
• BROWN, JOHN GEORGE (1831— )
• BROWN, ROBERT (1773-1858)
• BROWN, SAMUEL MORISON (1817—1856)
• BROWN, SIR GEORGE (1790-1865)
• BROWN, SIR JOHN (1816-1896)
• BROWN, SIR WILLIAM, BART
• BROWN, THOMAS (1663-1704)
• BROWN, THOMAS (1778-1820)
• BROWN, THOMAS EDWARD (1830-1897)
• BROWN, WILLIAM LAURENCE (1755–1830)

BROWN

See also:

• IRON [symbol Fe, atomic weight 55.85 (0=16)]

IRON ORE  , a natural ferric hydrate named from the Gr. ketgiav (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 . It is sometimes called brown haematite . Limonite is a ferric hydrate, conforming typically with the formula Fe403(OH)6, or 2Fe2O3.3H2O . Its hardness is rather above 5, and its specific gravity varies from 3.5 to 4 . In many cases it has been formed from other iron oxides, like haematite and magnetite, or by the alteration of pyrites or chalybite . By the operation of -meteoric agencies, iron pyrites readily pass into limonite often with retention of external form; and the masses of " gozzan " or gossan " on the outcrop of certain mineral-veins consist of rusty iron ore formed in this way, and associated with cellular quartz . Many deposits of limonite have been found, on he:ng worked, to pass downwards into ferrous carbonate; and crystals of chalybite converted superficially into limonite are well known . Minerals, like glauconite, which contain ferrous silicate, may in like manner yield limonite, on weathering . The ferric hydrate is also readily deposited from ferruginous waters, often by means of organic agencies . Deposits of brown iron ore of greateconomic value occur in many sedimentary rocks, such as the .

Lias, Oolites and Lower Greensand of various parts of England . They appear in some cases to be altered limestones and in others altered glauconitic sandstones . 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 "; and in like manner it is the agglutinating agent in many conglomerates, like the South African " banket," where it is auriferous . In iron-shot sands the limonite may form hollow concretions, known in some cases as " boxes." The " eagle stones " of older writers were generally concretions of this kind, containing some substance, like sand, which rattled when the hollow nodule was shaken . Bog iron ore is an impure Iimonite, usually formed by the influence of micro-organisms, and containing silica, phosphoric acid and organic matter, sometimes with manganese . The various kinds of brown and yellow ochre are mixtures of limonite with clay and other impurities; whilst in umber much manganese oxide is present . Argillaceous brown iron ore is often known in Gel-dimly as Thoneisenstein; but the corresponding term in English (clay iron stone) is applied to nodular forms of impure chalybite . J . C . Ullmann's name of stilpnosiderite, from the Greek yr X,ryos (shining) is sometimes applied to such kinds of limonite as have a pitchy lustre .

Deposits of limonite in cavities may have a rounded

surface or even a stalactitic form, and may present a brilliant lustre, of blackish colour, forming what is called in Germany Glaskopf (glass head) . It often happens that analyses of brown iron ores reveal a larger proportion of water than required by the typical formula of limonite, and hence new species have been recognized . Thus the yellowish brown ore called by E . Schmidt xanthosiderite, from YawBos (yellow) and old,tpos (iron), contains Fe20(OH)4, or Fe2O3.2H20; whilst the bog ore known as limnite, from Xt w,t (marsh) has the formula Fe(OH)3, or Fe2O3.3H2O . On the other hand there are certain forms of ferric hydrate containing less water than limonite and approaching to haematite in their red colour and streak: such is the mineral which was called hydrohaematite- by A . Breithaupt, and is now generally known under R . Hermann's name of turgite, from the mines of Turginsk, near Bogoslovsk in the Ural Mountains . This has the formula Fe40i(OH)2, or 2Fe203•HzO . It probably represents the partial dehydration of limonite, and by further loss of water may pass into haematite or red iron ore . When limonite is dehydrated and deoxidized in the presence of carbonic acid, it may give rise to chalybite .