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116 GEOGNOSY. ~ {Bape 
lakes, under marshy ground, or within fissures and cavities of rocks. 
Some of the iron ores might be placed with the schistose rocks; — 
but they are taken here for convenience. 
Hematite (red iron-ore), a compact, fine-grained, earthy, or 
fibrous rock of a blood-red to brown-red colour, but where most 
crystalline, steel-grey and splendent, with a distinct cherry-red 
streak. Consists of anhydrous ferric oxide, but usually is mixed with 
clay, sand, or other ingredient, in such varying proportions as to 
pass, by insensible gradations, into ferruginous clays, sands, quartz, 
or jasper. Occurs as beds, huge concretionary masses, and veins 
traversing crystalline rocks ; sometimes, as in Westmoreland, filling 
up cavernous spaces in limestone. 
Limonite (brown iron-ore), an earthy or ochreous, compact, © 
fine-grained or fibrous rock of an ochre yellow to a dark-brown colour, 
distinguishable from hematite by being hydrous and giving a 
yellow streak. Occurs in beds and veins, sometimes as the result 
of the oxidation of ferrous carbonate, also abundantly on the floors 
of some lakes and under marshy soil, where it forms a hard brown 
crust upon the impervious subsoil (bog iron-ore), Found like- 
wise in oolitic concretions sometimes as large as walnuts, con- 
sisting of concentric layers of impure limonite with sand and clay 
(Bohnerz). See p. 174, and Book III. Part II. Section iii. 
Spathic Iron-ore, a coarse or fine crystalline aggregate of 


the mineral siderite or ferrous carbonate, usually with carbonates of — 
calcium, manganese and magnesium; has a prevalent yellowish or 
brownish colour, and when iresh, its rhombohedral cleavage faces — 
show a pearly lustre, which soon disappears as the surface is oxidised 
into limonite. Occurs in. beds and veins, especially among older 
geological formations. ‘The colossal Erzberg at Hisenerz in Styria, 
which rises 2600 feet above the valley, consists almost wholly of 
siderite." 
Clay-ironstone (Spheerosiderite), a dull brown or black com- 
pact form of siderite with a variable mixture of clay, and usually 
also of organic matter. Occurs in the Carboniferous and other 
formations in the form either of nodules, where it has usually been 
deposited round some organic centre, or of beds interstratified with 
shales and coals. It is more properly described at p. 175, with the 
organically derived rocks, 
Magnetic iron-ore, a granular to compact aggregate of 
magnetite, of a black colour and streak, more or less perfect metallie 
lustre, and strong magnetism. H. 5°5 to 6°5, Gr. 4:9 to 5-2. Commonly 
contains admixtures of other minerals, notably of hematite, chrome- 
iron, titanic-iron, pyrites, chlorite, quartz, hornblende, garnet, epidote, 
felspar. Occurs in beds and enormous lenticular masses (Stécke) 
among crystalline schists. Thus among the gneisses of Norway lies 
the iron mountain of Gellivara in Luleo, Lappmark, 16,000. feet long, 
8000 feet broad, and 2000 feet high. 
 Zirkel, Lehrb. i. p. 345 
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