78 



Case 69. isolated crystals may often be detected in gold and silver ores, 

 e.g., that from Terranderie, Burragorang. Sometimes the 

 angles of the cube are cut off by faces of the octahedron, as 

 shown by 1220 from Mount Stewart, and also in case 33. 



t^^ AJ 



B C 



Crystals of Pyrite. 



A. Cube. B. Octahedron. C. Cuhe, witli octahedron. 



D. Pentagonal 

 dodecahedron. 



Yery frequently crystals of pyrites become oxidised by ex- 

 posure to the atmosphere. In this way the sulphur passes off as 

 sulphuric acid, and the iron remains as hydrated oxide, some- 

 times retaining the crystalline form of the original , pyrites most 

 perfectly {pseudomorpJious replacement):^ Several instances of 

 this replacement will be found in the Gold cases (see p. 32). 

 The sulphuric acid sometimes found in mine waters, v/hich so 

 quickly corroders iron pipes, arises in this way. 



2818, Tibooburra, shows a band of j^yrites with a thick crust 

 of oxide. 



5188, Wattle Flat, is tarnished, very closely resembling gold. 

 The cubic crystals are, however, very distinct under a lens, and 

 should prevent any mistake. 



5470, Bungonia, shows aggregations of cubes forming pretty 

 little rosettes. 



9199, Consols Mine, Broken Hill, has a curious surface irides- 

 cence. 



2816, Mount Macdonald : an irregular piece of chlorite, coated 

 with pyrites on every side. 



* The "Devil's dice" of the miners. 



