INDUSTRIAL MINERALS OKES DIAGRAM 19 227 



Diamonds and precious stones. Most precious stones are only 

 valuable and esteemed on account of their rarity. But the dia- 

 mond is the hardest known substance, and scratches all others. 

 It is therefore used to cut glass. There are no diamonds found 

 in Europe, but they are generally found in gold producing coun- 

 tries, such as the East Indies, America, and South Africa. They 

 are generally found in the gravel of river-beds, but they must 

 be cut in facets to give them lustre. 



Peat. Peat is not, strictly speaking, a mineral. It is a deposit 

 of dead plants which collect in the waters of marshes, and on 

 clayey flats which have no outlet for the rain. The plants and 

 mosses grow one above another, and finally form a compost 

 which burns readily when dried. This compost is then removed 

 in clods and put to dry in the sun. They shrink very much, and 

 then form a good combustible, which has only the inconvenience 

 of producing much ash. 



Guano. Guano is only found in the Chinchas Islands, off 

 Peru, and is brought from thence to be used as manure. It is a 

 yellowish earth with a very strong odour. Remains of the 

 feathers and bones of birds are often found in it, and it is be- 

 lieved to be chiefly composed of the dung of sea-fowl, which have 

 frequented these islands for a long period. Guano is one of the 

 best manures known, but it must be mixed with earth or other 

 substances before it is used, or else it would be too strong, and 

 destroy the crops instead of improving them. 



OEES. 



Those productions of the earth from which metals are ex- 

 tracted are called ores. It is rare to find metals existing pure in 

 a natural state, although some are met with in this condition. 

 Generally they are completely unrecognisable, and are only ob- 



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