TO DETECT MINERALS BY THEIR COLOUR, ETC. 35 



MINERALS OF UNMETALLIC LUSTRE. Continued. 



Also emerald nickel, silicate of nickel, and silicate of copper. 

 Also certain chromium and uranium compounds, certain phosphates 

 and chlorides, arsenate of copper, chloride of copper, silicates of 

 magnesia, &c., on surface nickel ore, green stains may be noticed. 

 Many other minerals, such as silicate of magnesia, have a greenish 

 tinge, also phosphate and chloride of lead, sulphate of copper, and 

 certain phosphates, &c. 



Blue 



Malachite and azurite Blue 



Bluish. 



The specific gravity of a rock can often be approximately 

 known by weighing it in the hand, and comparing it with 

 an equal bulk of some other familiar rock ; but to accurately 

 obtain the specific gravity of a mineral, a fragment of it 

 should first be weighed in air, then in water (which can be 

 done by suspending it to the scale of a balance and im- 

 mersing it in water). The weight in air, divided by the 

 weight in air minus the weight in water, gives the specific 



weight in air 



Tavitv o (JT " 



weight in air weight in water. 



But this method is more for the scientist than the ordinary 

 prospector. 



The colour and appearance of the line or furrow on the 

 surface of a mineral, when scratched or rubbed, is called the 

 streak, which is best obtained by means of a hard tempered 

 knife or a file. If the mineral is soft, it may be rubbed on 

 a piece of rough porcelain. Those parts which have been 

 much weathered should not be chosen. 



To discover the hardness of a mineral, it is necessary to 

 try and find out which of the typical specimens of the scale 

 of hardness (commencing with the hardest and proceeding 

 to the lowest) is scratched by it. 



