COPPER ORES. 45 



impart a green colour to the outer one. Copper compounds 

 are, for the most part, soluble in nitric acid. If a piece of 

 polished iron or the bright point of a penknife be dipped 

 into the acid solution, it will be slightly coated with metallic 

 copper if any exist in the ore. Ammonia added to an acid 

 solution affords a green colour, and, in excess, a blue one. 

 Many copper minerals can be dissolved in citric acid, some 

 in cold, others in a boiling solution, and afford a greenish 

 colour. A penknife blade (cleany placed in the solution is 

 covered with a copper film. Some, such as copper pyrites, 

 may be dissolved in a boiling solution of citric acid and 

 nitrate of soda. In the absence of a blowpipe or chemical 

 apparatus, the presence of copper in a substance may be 

 detected in this way : First, roast the mineral and drop it, 

 when hot, into some grease and expose it to the heat of a 

 flame, which will show a green colour if copper exists. Or, 

 if the mineral be well powdered, mixed with some fat and 

 salt, and placed in the fire, the presence of copper will be 

 known by the blue or green colour. If the powdered 

 mineral be mixed with a little charcoal and roasted for an 

 hour, and then vinegar be poured on it and allowed to 

 remain for a day or so, copper will produce a blue colour, 

 afterwards becoming green. 



In a copper-bearing lode the black oxide, sometimes red 

 oxide and green carbonate, may be noticed in the cavities 

 of the surface quartz. 



Native Copper. 



Found in treelike, mosslike, threadlike shapes, in octahe- 

 dral crystals, grains, &c. 



Colour copper red. 



Is ductile and malleable. 



H. 2-5 to 3; S.G. 8-5 to 8-9. 



Can be tested by the blowpipe or chemicals like other 

 copper ores. Usually carries silver. Found chiefly in 

 North and South America, also in Cornwall, Wales, &c. 



Copper Glance (vitreous copper ore). 



Crystallization rhombic prisms. Is slightly sectile. 

 Colour blackish grey, tarnishing to blue or green. 



