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See also:LIMONITE, or See also:
See also:Lias, Oolites and See also:Lower See also:Greensand of various parts of See also:England
.
They appear in some cases to be altered limestones and in others altered glauconitic sandstones
.
An oolitic structure is sometimes See also:present, and the ores are generally phosphatic, and may contain perhaps 30% of iron
.
The oolitic brown ores of See also:Lorraine and See also:Luxemburg are known as " minette," a diminutive of the See also:French mine (ore), in allusion to their See also:low content of See also:metal
.
Granular and concretionary limonite accumulates by organic See also:action on the See also:floor of certain lakes in See also:Sweden, forming the curious " See also:lake ore." Larger concretions formed under other conditions are known as " See also:bean ore." Limonite often forms a cementing See also:medium in ferruginous sands and gravels, forming " See also:pan "; and in like manner it is the agglutinating See also:agent in many conglomerates, like the See also:South See also:African " See also:banket," where it is auriferous
.
In iron-shot sands the limonite may form hollow concretions, known in some cases as " boxes." The " See also:eagle stones " of older writers were generally concretions of this See also:kind, containing some substance, like See also:sand, which rattled when the hollow nodule was shaken
.
Bog iron ore is an impure Iimonite, usually formed by the See also:influence of micro-organisms, and containing See also:silica, phosphoric See also:acid and organic See also:matter, sometimes with See also:manganese
.
The various kinds of brown and yellow ochre are mixtures of limonite with See also:clay and other impurities; whilst in See also:umber much manganese See also:oxide is present
.
Argillaceous brown iron ore is often known in Gel-dimly as Thoneisenstein; but the corresponding See also:term in See also:English (clay iron See also: Deposits of limonite in cavities may have a rounded See also:surface or even a stalactitic form, and may present a brilliant lustre, of blackish colour, forming what is called in See also:Germany Glaskopf (See also:glass See also:head) . It often happens that analyses of brown iron ores reveal a larger proportion of See also:water than required by the typical formula of limonite, and hence new See also:species have been recognized . Thus the yellowish brown ore called by E . See also: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 (See also:marsh) has the formula Fe(OH)3, or Fe2O3.3H2O . On the other See also: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 . See also: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 . |
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