80 THE MINERALS OF TASMANIA. 



augite of fair size may be collected in quantity near the Rail- 

 way Bridge which spans the Hellyer River. At the Cole- 

 brook Mine, iiralite reaches a remarkable state of develop- 

 ment. The average specimens of hornblende, tremolitei, 

 and actinolite are found, while beryl of comparatively 

 enormous size, but dull colouration, occurs in a pegmatite 

 dyke about 500 yards north of the Republic Mine, Ben 

 Lomond. It is associated with extremely fine and perfect 

 crystals of an almost white orthoclase. the individuals of 

 which sometimes reach several inches in length, and are 

 occasionally twnined. 



Among the unisilicates, axinite is to the front as a pro- 

 minent species. It is almost solely confined to the igneous 

 formation known as the Colebrook Mine. It is in large 

 violet-coloured plates, freely interspersed in association Vvith 

 calcite, pyrrhotite, datolite, arsenical and iron pyrites. 

 Garnet of several sub-species is occasionally met with, and a 

 new manganese variety, which has been named Johnston- 

 tite, has been discovered in the peculiar rocks at Port 

 Cygnet. At Hampshire Hills there is an extensive develop- 

 ment of weli-crystallised idocrase, which, practically, illus- 

 trates a contact phenomenon. The white silvery lithia 

 variety of muscovite, which is termed zinnwaldite, is plenti- 

 ful in the tin-districts on the North-East Coast. Of the 

 whole group of felspars, as occurring in this State, orthoclase 

 has its highest crystallographic development. In the tra- 

 chj'-tes and phoiiolites of Port Cygnet wonderfully-fine 

 crystals are easily broken free of the rock, and these often 

 show both Baveno and Carlsbad twinning; its variety, sani- 

 dine, also occurs at the same locality in almost colourless 

 glassy crystals. A massive white scapolite has been un- 

 earthed at Beaconsfield. Saussurite is abundant in the 

 altered gabbros of the Heazlewood district'. In th'e alluvial 

 tin-drifts of the North-East and at Shekelton, near Table 

 Cape, the zircon occurs in extreme profusion. Many from 

 the former locality are really nice gem-stones when properly 

 cut, and are reported to be among the most lustrous in the 

 world. In the rock-forming section of the group we can 

 claim hauynite, nephelite, and melilite, all old-world forms 

 only recently identified as occurring here, the last giving its 

 prefix to a basaltic rock at Shannon Tier. 



Here we must note those remarkable pellets of mystery, 

 the only known form of acidic volcanic glass which has, so 

 far been discovered in the Island, and which are usually 

 termed obsidian buttons, but more recently obsidianites and 

 australites. Whence came they, and why have they been 

 so long neglected by our local geologists and physicists? 



