154 THE MINERALS OF TASMANIA. 



Cavities in the ore-body are sometimes found completely- 

 lined with the substance, with which the sulphide ores are 

 intermixed. It also forms seams and masses of the char- 

 acteristic rose colour. 



278. RuTiLE (Binoxide of Titanium). 



This mineral crystallises in the tetragonal system, and is 

 one of the modifications of the trimorphous body Ti O^ ; 

 the others being brookite and anatose. 



Titanium dioxide has been formed artificially by the 

 reaction of titanium fluoride and water vapour. The pro- 

 cess is therefore really analogous to that which has yielded 

 cassiterite ; indeed, stannic oxide and titanic oxide stand in 

 close chemical relationship. Pneumatolytic action may thus 

 be invoked as a possible explanation of the genesis of these 

 minerals (Rudler). The species of titanium oxide have 

 been formed artificially, and are dependent upon various 

 temperatures, rutile being formed at a red heat ; at a tem- 

 perature such as would volatilise zinc brookite was pro- 

 duced ; and at a temperature just below that at which 

 cadmium may be volatilised anatase results. This mineral 

 is abundant in the alluvial drift, but much rounded, at 

 Brown Plains ; about the south-west base of Mt. Lyell ; in 

 waterworn fragments, and occasionally as well-formed 

 crystals, Clayton Rivulet ; in red-brown to almost black 

 capillary bunches penetrating quartz crystals, Moorina and 

 other places. 



Occurs in large quantities in grains and slightly water- 

 worn crystals up to J-inch in length in surface-drift, and 

 enclosed in a brecciated sandstone on the top and slope 

 of a hill situated a short distance from Hamilton-on-Forth. 

 The crystals are usually well-formed, including angulated 

 twins, but have mostly rough faces. The colour varies 

 from light to dark-reddish brown. Metagenic twins are 

 of frequent occurrence. The variety called nigrine, of a 

 very dark-brown to black colour, occurs abundantly m 

 small waterworn grains and imperfect crystals in drift at 

 Rocky Cape. It is very plentiful in auriferous drift at 

 Lymington, Port Cygnet. At the Penguin River and 

 vicinity it is fairly common. 



279. Sandbergerite = Kupferblende. (See Tennantite.) 



280. Sanidine (The Glassy Variety of Orthoclase). 



This is the glassy variety of potash felspar that occurs 

 in imbedded crystals in various igneous rocks. Plentiful 

 as fine bold crystals, often showing zonal growth, in the 



