444 SCIENTIFIC RECREATIONS. 



presence is necessary in all blast furnaces. The most important of the iron 

 group of minerals are MAGNETIC IRON (magnetite), or 

 loadstone. This mineral occurs in Sweden and North 

 America, and is found in primary rocks, and in Scandi- 

 navia forms mountains. It crystallizes in the regular 

 (octahedron) system, and often in the form in illustration 

 in the margin. It is highly magnetic, as its name 

 implies. 



Fig. 4 72 .-Magnetic iron. Native iron very rarely occurs, and then only in thin 



layers. The most extraordinary specimens are those termed meteoric iron, 

 which fall from the atmosphere in great masses ; and the meteoric stones, 

 which contain ninety per cent, of iron, together with other constituents in small 

 quantities viz., nickel, cobalt, copper, manganese, carbon, sulphur, 

 arsenic, etc. 



Red hematite crystallizes in the hexagonal system. It possesses much 

 the same (chemical) constitution as corundum 

 (q. v.}. It is brightly metallic, and shows a 

 red streak. It occurs in various forms, as 

 iron glance or specular iron, which is found 

 in Sweden and Russia ; micaceous iron, blood- 

 stone, clay, ironstone, etc. 



Brown hematite has not been found in 

 crystals, but brown ironstone (fibrous) is cry- 

 stalline. The earthy brown, containing clay, 

 gives us yelloiv ochre and umber. Pea-iron 

 ore and "morass" or "bog" ore also belong 

 to this class. Limonite is the name given to 



r i.- i 11 Fig. 473. - Native oxide of iron. 



these more recent formations, of which yellow 

 ochre is a pure specimen. 



The combinations of iron with sulphur (pyrites) are also important. 

 iron pyrites and .magnetic iron pyrites are two which may be mentioned. 

 The latter first. 



Magnetic iron pyrites (or pyrrhotiti) crystallizes in six-sided prisms, and 

 is attracted by the magnet. The composition of this mineral has not been 

 exactly ascertained, and no chemical formula has been found for it. 



IRON PYRITES (bisulphide of iron) is known as cubic pyrites, yellow 

 pyrites, and mnndic. It is generally found in the regular system of crystals, 

 either as a cube or as a pentagonal dodecahedron. (See first system of crystals, 

 ante') Its colour is yellowish. It is known also as green vitriol when 

 oxidised, and forms beautiful green crystals (copperas). This salt is used 

 in the preparation of Prussian blue and violet dyes. With gallic acid it 

 makes ink. 



There are many other "ferruginous" minerals, such as vivianitc, green 

 ironstone, white iron pyrites, arsenical pyrites, or mispickel, etc. 



