94 DESCRIPTIONS OF MINERALS. 



Iror>. occurs in the state of sulphide (very common, but not 

 useful as an ore of iron), of arsenide, sulph-arsenide, oxide (the 

 common ores of iron), carbonate (useful ore), sulphate, arsen- 

 ate, phosphate, silicate. 



JIauganese occurs in the state of sulphide (rare), arsenile 

 (rare), oxide (the common ores), carbonate, sulphate, phosphate, 

 bilicajte. 



I. MIXEEALS COXSISTIXG OF THE ACIDIC 

 ELE^IE^TS. 



Oxygen might properly be included in this section, since it 

 occurs native in the atmosphere mixed with nitrogen, consti- 

 tuting 21 per cent, of it. But this mention of it is all that is 

 necessary. The ternary compounds, in which, as in sulphuric 

 acid, hydrogen is the basic element, are here included. Chlor. 

 ine, bromine, and iodine do not occur native, and neither do their 

 oxides, nor any compounds with acidic elements, and hence these 

 elements are not represented under this division. The same is 

 true of selenium and chromium of the sulphur group, and of 

 vanadium, tantalum, and columbium of the arsenic group. 



L SULPHUR GROUP. 



Native Sulphur. 



Trimetric. — In ac i- .te octahedrons, and secondaries to this 

 form, with imperfect octahedral cleavage. 1 A 1 (in same pyra- 

 1. 2. 



mid) = 10i)° 25' and 85° 07'; lAl (over base) = 143° 23\ 

 Also massive. 



Color and streak sulphur-yellow, sometimes orange-yellow, 



