68 MINERALOGY. 
It is opake, black, and hyacinth-red, with slight translucency in the lamine. 
It is brittle, and its fracture is conchoidal. When pure, specular oxyde is an 
unmixed oxyde of iron, containing 69.34 per cent. of iron, and 70.66. of 
oxygen. Its crystals have an acute rhombohedron ( pl. 34, jig. 30) as the 
primary shape, and occur generally with planes of derivative forms ( figs. 28, 
25,31, and 40). Specular oxyde of iron occurs also in aggregations of highly 
lamellar irregularly curved leaves, of a shiming black color, known as 
micaceous iron ore: pl. 34, fiy.1, represents a mineral coated with this 
micaceous ore. 
A second form of oxyde of iron is more important on account of the 
greater masses in which it is found. This is the hematite ore. Red 
hematite occurs, like specular iron ore, in beds and veins in the older rocks, 
particularly in clay slate, mica slate, gneiss, and granite ; also in transition 
rocks in clay slate, and in grauwacke. Hematite is of a steel-grey, cherry- 
red, brownish, and blood-red color, and occurs under the most diversified 
circumstances of distribution. The purer hematites are frequently of a 
highly fibrous texture, and reniform or kidney-shaped ( fig.20). It is some- 
times found in cylindrical scaly masses, as in fig. 11, as also amorphous, dull, 
earthy, and, in the latter form, mixed with various rocks. With clay it 
forms red ochre, and with common limestone, the calcareous iron ore. Not 
less important are the brown and yellow iron ores. These are combinations 
of oxyde of iron with water, and furnish excellent ores for reduction. Fig.9 
exhibits a form of fibrous brown hematite, such as is frequently found in the 
Hartz, and fig. 5, another variety of its occurrence. The iron ores among 
which the oxydes are pre-eminent, always contain a considerable proportion 
of their gangue or matrix. The manufacture ef iron from its ore consists 
of two distinct operations, the mechanical separation of extraneous matters, 
as far as possible, and the reduction of the oxyde to the metallic state. The 
iron ore is introduced in alternate layers with coal into a furnace several 
stories high, into the lower part of which a powerful blast is continually kept 
up by a blowing apparatus. By this means the contents of the furnace are 
brought to, and kept at, a white heat. At this temperature the oxygen of 
the iron combines with the carbon of the coal, and forms carbonic oxyde and 
acid, the iron being left in a metallic state. The accompanying rock 
is melted by adding the necessary flux. In this way the whole contents of 
the furnace become perfectly liquid, the iron, from its greater density, 
occupying the lower part. By making certain apertures in the clay stopping 
up the bottom of the furnace, either the slag or the melted iron may be 
drawn off. 
The iron thus, obtained is still very impure, and contains especially a 
good deal of carbon in the state of carburet of iron; it is now known as 
cast iron or pig iron. This pig metal is purified. by remelting in a melting, 
or run out furnace ; after which it is puddled, and hammered out into bars 
in forges. Bar iron still contains carbon, the amount not over one half per 
cent.,.and not materially affecting its malleable properties. On the other 
hand, a slight per-centage of phosphorus (also of silicon, according to some 
authorities) renders the iron cold short ; and the presence of sulphur, arsenic, 
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