Serpentine Area and RhyoUtes. 259 



One feature worthy of note can be observed in several places, 

 notably a few chains west of the corundum outcrop on Kangaroo 

 Spur, and again in a small gully to the west of the chromite 

 occurrence, and that is the character of the dark greenish-black 

 peridotite serpentine. At both these spots the appearance sug- 

 gests an agglomerate, but more investigation is required to 

 decide whether this is the case or whether the features are 

 simply due to a particular type of weathering, simulating the 

 fragmental character of an agglomerate. 



Special Minerals. 



The following require particular attention: — 



(1) Corundum. 



(2) Chromite. 



(3) Common Opal. 



(1) Corundum.— -This was first found about the middle of last 

 year by two bushmen, Macfarlane and Piden. Specimens were 

 sent to the Mines Department, and also to the writer. The 

 occurrence at once attracted the attention of Mr. Dunn, Director 

 of Geological Survey, hence the flying visit by Mr. Dunn and 

 Professor Skeats. 



The corundum was found to occur sporadically in lumps up to 

 about 3 cwt. in size, at two spots not far distant, namely, the 

 Monument Gap and a little to the east, on the Kangaroo Spur, as 

 indicated on the map. The mineral is violet in colour, somewhat 

 translucent, compact and massive, rather tough, and breaking 

 with a somewhat splintery fracture. A certain amount of a gi'een 

 amorphous mineral is present in small quantity, as impurity. 

 This is probably a hydrated silicate of alumina, coloured with 

 oxide of chromium. 



Thin sections show the corundum as irregular patches of a 

 violet colour, with numerous long prisms of the same mineral, 

 forming a somewhat mesh-like appearance. Pleochroism is dis- 

 tinct. A small amount of interstitial material shows low polari- 

 zation colours, and as the analysis show^s very little magnesia it is 

 probably some form of hydrated silicate of alumina. 



A massive corundum has since been found in the Heathcote 

 area by Professor Skeats, and a slide of this shows somewhat 



18a 



