79 



Lumps or nodules of pyrites are frequently found in shale and Case 69, 

 other sedimentary rocks ; these are of secondary origin, (See 

 4362, Mount Poole, and Structure case 113.) 



1373, Thackeringa, illustrates the sUchensides so frequently 

 met with in mining (see page 173). These sliekensided surfaces 

 are often subsequently coated with a thin film of pyrites (see case 

 138), or the pyrites itself may become polished, as in this 

 instance. 



3743, Cullen BuUen. Pyrites is sometimes found in small 

 quantities in coal ; its presence is highly detrimental. 



10158, Lobb's Hole, Yarrangobilly, shows good crystals. This Marcasite. 

 form of iron pyrites is characterised by its ready decomposition, 

 and may oftea be noticed in gold ores, e.g., the Mount Dromedary 

 ore. 



Magnetic pyrites di:ffers from ordinary iron pyrites in contain- Pyrrhotite. 

 ing a higher proportion of iron. It is bronzy in colour, and 

 readily attracted by a magnet, whence its name. A massive 

 mineral frequently met with in ore deposits ; it is very seldom 

 gold-bearing. 



Specimens are exhibited from Blayney, Bolivia, The Pinnacles, 

 Glen Innes, Tent Hill, Macleay Eiver ("Willi Willi), &c. 



ARSENIC. 



Arsenic is used in many ways. It forms the basis of the Case 68. 

 sheep-dips used in Australia ; and there is some demand for rich 

 arsenical ores. 



A black, hard mineral, with a mammillated crust, breaking Native 

 with a grey, finely-crystalline fracture. ' arsenic. 



Mispiclcel : sulph-arsenide of iron; tin-white in colour ; Arsenical 

 frequently emits an arsenical odour when struck with a hammer, Py^"®^- 

 and the fumes can be detected by their odour when the mineral 

 is slightly heated. It is frequently associated with the precious 



