50 MINERALS OF TASMANIA. 
160. OLIVINE—See CurysotiTe. 
161. OSMIRIDIUM (an Alloy of Osmium and Iridium). 
Found as thin, shining, tin-white scales of small size, with Gold 
and Iridium, in alluvial drift. Atthe Badger Gold diggings, west 
of the Savage River, which is a tributary of the Pieman, it was 
obtained in considerable quantity of the characteristic form, but 
occasional pieces were obtained of unusually large size—one 
example measuring about % of an inch in diameter. At the 
Castray River fine scaly pieces are often obtained with gold and — 
chromic-iron sand. 
King River; Queen River; at Dundas it has been obtained 
attached to pieces of quartz; Brown’s Plain and other places 
near the Pieman River. 
This mineral as occurring in this island and in Australia 
invariably contains a small quantity of Platinum in alloy. 
162. OBSIDIAN (Volcanic Glass). 
Occurs in small quantity at the Mersey River; stated to exist 
in Gould’s Country ; it has been found in circular and concave 
or button-like flakes of an intense black colour in stanniferous 
drift, apparently igneous ejectamenta, Thomas’s Plains; as 
massive lumps with Pitchstone and Olivine. Sheffield. 
163. OLIGOCLASE (Soda Felspar). 
This is a much scarcer form of Felspar than Orthoclase. It is 
usually of pale tints and more or less translucent. 
In Porphyry, Blue Tier. 
164. PHARMACOSIDERITE (Arsenate of Iron). 
The primary form of crystallization in this mineral is the cube, 
by which character it may be separated from its chemical ally 
Scorodite—which is rhombic. In colouration it ranges through 
many shades of olive-green to brown. It is sectile, resinous, and 
is commonly found in the amorphous state or earthy. 
Waterhouse. 
165. PYROMORPHITE (Chlorophosphate of Lead). 
This mineral can be readily identified by its crystallization, 
which is in hexagonal prisms, usually aggregated together im 
bunches and masses. In colour it shows gradations through 
many shades of green, rarely brown to almost white. 
At the Godkin mine, Whyte River, it occurs in minute crystals, 
and as large massive amorphous earthy lumps, which are generally — 
mixed with a kaolinic clay and more rarely Pyrolusite; at the 
Heazlewood mine it is found in microscopic crystals, which are 
almost colourless to the normal green prisms; the Sylvester mine 
at Zeehan has produced the largest and most beautiful masses of 
