310 TERMINOLOGY. . 210. 811. 



. 210. MAGNETISM. 



Some minerals act upon the magnetic needle, if 

 they are brought within the sphere of its attraction. 

 Others become magnets themselves. These pheno- 

 mena are made use of as characters, under the 

 name of Magnetism. 



The only minerals hitherto known, which exercise a con- 

 eiderable action upon the magnetic needle, are the octahe- 

 dral Iron, and the octahedral Iron-ore. Rhombohedral 

 Iron-ore, rhombohedral Iron-pyrites, and several others, 

 likewise act upon it, but with less energy. 



Instead of a needle, the magnetic bars may be applied 

 in examining minerals, which in this case must be convert- 

 ed into a fine powder, in order to extract from them such 

 particles as possess magnetic properties. 



. 211. ELECTRICITY, 



Several minerals produce electric phenomena; 

 some of them by friction, others by pressure, others 

 by communication, and others by heat. Some are 

 idio-electric ; others are conductors of electricity. 

 These phenomena may be usefully applied as 

 characters of minerals. 



Vitreous electricity is produced by friction in most mi- 

 nerals of the orders Gem, Spar, Mica, Bary te, &c. in seve- 

 ral Haloides, and even in Salts. In the same way those of 

 the orders Sulphur, Resin, and Coal, shew the phenomena 

 of resinous electricity. As conductors of electricity, we 

 may notice the minerals of the orders Metal, Pyrites, and 

 Glance. Those of the orders Blende, Ore, and several 

 others, do not appear quite uniform in this respect. 



Heat produces electric phenomena in prismatic Topaz, 

 in rhombohedral Tourmaline, in prismatic Kouphone-spar, 



