1T4 CLASSIFICATION OF MINERALS, 



in inventing the language of mineralogy ? 7. What was necGssary 

 for this purpose ? 8. Why \vere they called external charactera r 9. 

 What are the three other divisions of the characters of minerals ? 10. 

 What are the general external characters of minerals ? (See Appen- 

 dix.) 11. -Pa r^icw/arextem^nl characters .' 12. What farther descrip- 

 tions are given f 



LESSON 77. 



Classification of Minerals. 



Lap'idary, one who deals in gems, or precious stones. 



Ductil'ity, a quality of certain bodies, in consequence of which 

 they may be drawn out to a certain length without fracture. 



Malleabil'ity, that property of metals which gives thorn the capa- 

 city of being extended and flattened by hammering. 



Minerals are usually arranged under four classes; earthy, 

 saline, inflammable, and metallic. The earthy minerals con- 

 tain all such as derive their qualities from the earths ; and 

 they are divided into genera, according to the particular 

 earth which predominates in each, or more properly, into 

 families, according to their resemblance in external charac- 

 ters, as the diamond family, the ruby family, talc family, and 

 others. The diamond, of which there is only a single spe- 

 cies, is the hardest and most beautiful of all the mineral pro- 

 ductions. When heated to the temperature of melting cop- 

 per, and exposed to a current of air, it is gradually but com- 

 pletely combustible. It is wholly converted into carbonic 

 acid, and therefore consists of pure carbon, as we have al- 

 ready mentioned. By means of diamond powder, this sub- 

 stance can be cut and polished upon a wheel in the same 

 way as any. other gems are v/rought by emery. It is ma- 

 nufactured by jewellers into brilliants and rose diamonds ; 

 and is employed by glaziers for cutting glass ; by lapidaries 

 for cutting and engraving on the hardest gems, and in the 

 finer kinds of clock work. Before the discovery of the 

 Brazilian mines, diamonds were much more rare, and of 

 course dearer than they have been since. .In the year 1730, 

 eleven hundred and forty-six ounces were brought to Europe ; 

 in consequence of which, the price of this article immedi- 

 ately fell three-fourths, and to prevent a still further depre- 

 ciation, the Portuguese government restricted the number 



