32 



tse 51. 2624, Mann Eiver : an instance o£ gold occurring in calcite. 



5547, Manilla : auriferous pyrites with a peculiar structure. 



6579 and others, Bingara : gold in serpentine associated with 

 such minerals as talc (2152) and chlorite (1135). In case 136, 

 near the door, is a block specimen of the serpentine with fine 

 gold coating the smooth surface. 



6969, Groklen Crown Eeef, Lunatic : Xative arsenic containing 

 gold. A specimen formerly in the collections, but unfortunately 

 stolen, showed free gold seated on the arsenic. 



7064, Millara Scrub, near Solferino, is very instructive. The 



pieces exhibited consist of brown oxide of iron (limonite). That 



they were at one time pyrites is shown by the crystalline form, 



and by the kernel of pyrites still remaining within one or two 



of the crystals. Gold is freely visible. Numerous other instances 



of this transformation will be referred to in this guide. 



The alteration of the original pyrites is the result of the action of 

 surface waters, and of the atmosphere. Under the influence of 

 oxygen (from the air) and moisture, the sulphur is converted into 

 sulphuric acid, and is removed in solution, while the iron is 

 oxidized and hydrated, and remains behind as limonite. The 

 process is technically described as a pneudomorjihous rejjlacement 

 of pyrites hy limonite. The resulting limonite cubes are known as 

 psc'udomorphs after limonite by the geologist. They are the 

 "devil's dice" of the miners. For other instances of pseudo- 

 morphous, replacement, see Students' Case 33. 



Timl)arra.— T\'\Q auriferous granite from Timbarra, represented 

 at the left hand end of this case, is particularly worthy of atten- 

 tion. That the rock is truly granite is evident enough, and that 

 it contains gold receives ocular demonstration from 8124 and 

 :2151. The gold occurs along a belt, several miles long, of a 

 granite plateau. The alluvial in the valleys draining this plateau, 

 which has resulted from the degradation of the granite, has 

 yielded much gold. The granite itself has been softened by 

 atmospheric weathering, for a depth of several feet. This soft 

 material, which is generally red or yellow in colour owing to the 

 oxidation of iron, is excavated and ground-sluiced ; the undecom- 

 posed portions being left standing in large masses. The average 



