122 THE WORLDS LUMBER ROOM. 



through from the surface. The iron oxide seems then to 

 have been dissolved out and carried away to the foot 

 of the range, where there are immense deposits of iron 

 ore.* 



West of Blue Ridge alumina is found in considerable 

 quantities, combined with, a small amount of iron and silica ; 

 but instead of being in the soft, sticky state of clay, it is 

 intensely hard, being, in fact crystallised. Were it not that 

 the crystals are all flawed, and therefore valueless as gems, 

 they might almost be called a mass of sapphires and rubies, 

 for many of them are coloured with the most beautiful tints 

 of pink, blue, and deep ruby. As it is, the mineral is 

 called corundum, and is most useful for grinding and 

 polishing, and, being much harder than emery, and prepared 

 at much less cost, is likely to be a formidable rival. Emery 

 itself is but another form of alumina, containing a large 

 admixture of iron, and is obtained chiefly from the decayed 

 rocks at Cape Emeri, in the island of Naxos.f 



The opaque stone, known as the Oriental turquoise, is 

 a phosphate of alumina coloured by copper. 



And thus from clay and mud we have come round to 



* The gneiss and granite rocks of Brazil are similarly decomposed to 

 the depth of 100 feet. 



f The hardness of the sapphire being 100, that of corundum is 77, and 

 the emery of Naxos, 46. By melting china clay with red lead, the silica 

 is extracted, and after exposure for several weeks to intense heat, the 

 mixture, on being allowed to cool, is found separated into two layers, the 

 upper, mainly silicate of lead and glassy-looking, the lower, crystalline, 

 and containing perfect, but colourless, crystals of alumina, which are 

 specimens of the corundum, and when coloured by the addition of iron, 

 cobalt, &c. , differ in no respect in composition or appearance from the 

 Oriental ruby and sapphire. 



