182 THE MINERALS OF TASMANIA. 



of felspar to topaz. Although topaz may be of secondary 

 origin, it may lend itself to decomposition, and then pass 

 into kaolin, micaceous minerals, or prosopite, with 

 which latter mineral it is not uncommonly associated. 

 It is obtained at several of the tin-mining districts of the 

 island, " of the finest water, and of a brilliancy scarcely 

 inferior to the diamond " (Bristow " Glossary of Mineral- 

 ogy," 1861, p. 383). It is found of all sizes. Specimens 

 have been obtained nearly 8 inches in length, and of per- 

 fect transparency. At Killiekrankie Bay, on the west side 

 of Flinders Island, it occurs in great profusion, both as 

 waterworn pebbles, and more rarely in fine, well-defined, 

 clearly-cut crystal forms. It occurs in stanniferous alluvial 

 drift, resulting from the detrital granite rock. Several 

 other minerals are common with it, including quartz, zircon, 

 and black tourmaline. The topaz is but rarely found in 

 situ ; it occurs in fissures and vughs associated with crystals 

 of felspar and quartz. The late C. Gould, at one time 

 Government Geologist (Pro. Roy. Soc. Tas., 1871, p. 60) 

 wrote that the topaz originated from pegmatite bands, vary- 

 ing in width from 1 to several fe-et, composed of the ordin- 

 ary Tertiary granite minerals highly magnified, the size of 

 the individual minerals being enormously increased, so 

 that the blocks of felspar, quartz, and even mica, occur up 

 to several feet in dimension. These appear to be the 

 scene of the most abundant source of the topazes, which 

 have crystallised out into natural cavities, from whence 

 they have been delivered by erosion." At Mt. Cameron 

 ^nd vicinity they are abundant, although generally much 

 waterworn, in the alluvial tin workings. They occur more 

 or less abundantly all through the north-eastern tin -pro- 

 ducing districts, Thomas' Plain, Moorina, and the Weld 

 River being noted localities. At Bell Mount and vicinity, 

 in the Middlesex district, topaz has been obtained some- 

 what abundantly, both in situ and in the tin drift. The 

 samples obtained in the porphyritic rock are usually 

 beautifully crystallised, with bright well-cut facets. They 

 often occur in bunches and groups interspersed with the 

 tin crystals. They are not in this locality so large as 

 many found in the vicinity of Mt. Cameron or at Flinders 

 Island. At the Shepherd and Murphy Mine they occur 

 in the lode-filling in close association with bismuthinite, 

 cassiterite, and wolframite, with abundance of highly 

 coloured fluorite and green talcose ^|)0(iumene. In- tlie 

 granitic alluvial wash of the Stanley River tinfield topazes 

 with sapphires are sometimes found, together with tin ore, 



