3 THE PROSPECTORS HANDBOOK. 



minerals assume the same or nearly the same shapes of 

 crystal ; and, again, certain particular minerals are found of 

 more than one shape. 



As examples of the first are carbonates of lime, lime and 

 magnesia, zinc, iron, where the angle of the rhombohedral 

 forms only vary between 105 and 108. 



Sulphur, iron pyrites, specular iron, carbon, are examples 

 of the second kind. 



In addition to the already-mentioned characteristics use- 

 ful in the determination of the nature of a particular mineral, 

 some peculiar properties belonging to certain minerals 

 should be noted. 



For instance, some iron, cobalt, and nickel ores are 

 attracted by the magnet ; some minerals such as fluor-spar, 

 topaz, carbonate of lead, quartz, and calc spar become 

 electrified by friction ; others such as calamine become 

 so when heated. Others, when rubbed, yield a peculiar 

 odour; some such as fluor-spar are phosphorescent, that 

 is, yield a peculiar light when heated ; while many possess 

 a characteristic taste. 



