286 MINERALOGY 



B.B. Fuses easily at 114.5 and burns with a blue flame, form- 

 ing sulphur dioxide. When pure, volatilizes entirely. Insoluble 

 in acids. Dissolves in carbon disulphide. 



General description. Crystals are pyramidal in habit, termi- 

 nated by the base, the two domes e and n, and the pyramids s ; 

 many other forms have been described, all of which are rare. Some 



FIG. 393. Sulphur Crystals from Girgenti, Sicily. 



crystals are sphenoidal in habit, indicating the holoaxial symmetry. 

 The best examples of sulphur crystals are found at Girgenti, Sicily, 

 where they occur associated with celestite and other sulphates. 

 More of ten the crystals are small or the sulphur is incrusted, massive, 

 or powdery, mixed with clay, marl, or other impurities. Sulphur 

 is a non-conductor of heat, and a peculiar crackling noise may be 

 noted when a crystal is held to the ear, in the hand, due to the un- 

 even heating ; in this way crystals often fall to pieces. 



Sulphur is deposited around volcanoes and solfataras, where it 

 is condensed from vapors or reduced by the interaction of SC>2 

 and H 2 S, or again by the oxidation of H 2 S. Many hot springs con- 

 tain H2S in solution which on oxidation deposits sulphur. In sedi- 

 mentary deposits sulphur js formed in the reduction of sulphates, 

 and is often associated therefore with celestite and gypsum. It 

 has also been observed in the cracks of galena, as at the Wheatley 

 mine, Pennsylvania. 



Deposits of sulphur in the United States are found in the Yellow- 

 stone Park, in a rhyolitic tuff ; at Black Rock, Utah ; at Cody, 



