CHAPTER IV. 



THE CHARACTER OF MINERALS. 



External Characteristics. Tables for determination of the nature 

 of a Mineral by noting its Colour, Lustre, and Streak. Specific 

 Gravity. Hardness. Crystallization. 



IN order to discover the nature of a rock, the mineralogist 

 may derive the necessary information by a careful study of 

 its external appearance and characteristics; the form of 

 crystallization, hardness, specific gravity, colour, streak (the 

 colour when scratched, or when rubbed on a piece of porce- 

 lain), &c., and also from its behaviour when exposed to the 

 action of chemicals or heat. 



When examining a mineral specimen, the prospector is, to 

 a great extent, guided by its colour. He may form a truer 

 estimate by also noticing the lustre and streak. But it must 

 be borne in mind that, for example, tinstone, though usually 

 found of a brownish or blackish colour, is sometimes grey. 

 Its streak, too, is not always brown, but sometimes grey, &c. 

 Cinnabar, too, is usually red, though occasionally brown or 

 brownish-black. 



The following table may be of some use in the examina- 

 tion of some of the most commercially useful minerals : 



METALS WITH METALLIC STREAK. 



