32 



CHELLAGOE GARNET ROCK 



from an outcrop near the Dorothy mine at Chillagoe, and 

 consisted of a crystaUine aggregate, the crystals being of 

 yellowish brown colour, and consisting mostly of the usual 

 rhombic dodecahedron. The cr\stals were carefully sep- 

 arated from cementing material (which, by the way, ap- 

 peared to be amorphous garnet), and were obtained 

 apparently clean. The analysi 



Silica (SiOg) 



Ferric Oxide (FegOg) 



Ferrous Oxide (FeO) 



Alumina (AlgOg) 



Manganese Oxide (MnO) 



Lime (CaO) (other than CaCO^) 



Magnesia (MgO) 



Combined water 



Calcium Carbonate (CaCOg) 



Moisture 



s resulted as follows :— 



38.10% 



18.79% 



1.00% 



9.75% 



0.22% 



31.06% 



Nil 



0.46% 

 0.57% 

 0.12% 



100.07% 



The carbonic acid (0.25%) was evidently due to admixed 

 calcite which had escaped in the cleaning of the crystals, 

 and it w^as therefore calculated to calcium carbonate. 



The ferrous iron was determined by the hydrofluoric 

 acid method. Triplicate assays gave identical results, 

 and a check made on ferrous ammonium sulphate gave an 

 accurate result. 



The loss on ignition (0.8%) was higher than anticipated 

 and pointed to the presence of combined water. As this 

 w^as of interest, in view of the generally accej)ted theory 

 that the formation of garnet took place under conditions 

 of moist heat, 1 determined the combined water in 2| 

 grammes, dried at 100° C, using series of calcium chloride 

 tubes placed before and after the ignition tube ; the result 

 w^as a gain equal to 0.46%. which is reported as combined 

 water. 



The specific gravity was found to be 3.429. 



Garnet Rock. — The garnet rock consists of garnet 

 mineral, eitlier by itself or, as is usually the case, mixed 

 with one or more other minerals. It is a matter of some 

 difficulty to say just what minerals are associated in the 

 Chillagoe district, though it may be said that hand speci- 

 mens usually show either calcite or amphibolite. When 



