INDUSTRIAL MINERALS ORES DIAGRAM 20. 229 



very useful in industry. We have mentioned that it can be 

 extracted from sea-weeds, but the greater part is manufactured 

 directly from salt. 



Diamonds and Precious Stones. Most precious stones are only 

 valuable and esteemed on account of their rarity. But the 

 diamond 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 countries, 

 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. 



Feat. 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 of a very strong odour. Remains of the feathers 

 and bones of birds are often found in it, and it is believed 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. 



ORBS. 



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. 



