Western Australia. 



153 



in section its characters more closely agree with tliose of a talc- 

 chlorite rock. An analysis made in the Survey Laboratory gave the 

 following results : — 



91-70 



Total 



100-55 



From the relatively high percentage of alumina and ferrous oxide, 

 it would appear that chlorite is present in fair amount. On the other 

 liand, as potash is absent there is no sericite. The silica percentage 

 is in the neighbourhood of that of the various epidiorites and 

 amphibolites, and, though not much reliance can be placed on this 

 as a criterion, it is probably that the rock has been derived from 

 some such original. 



7006 is almost identical with 3391. 



12240 is grey in colour and more or less granular, and witli 

 a soapy feel. In section it is composed of a mass of minute scales 

 and rods of a yellowish-green mineral v. ith rather high birefringence 

 and noticeable pleochroism, amongst which there seem to be other very 

 minute needles of a paler colour. Idiomorphic crystals of reddish 

 dusty carbonate are not uncommon. There are occasional fragments 

 of quartz, and a few small pieces apparently of felspar. An analysis 

 of the rock made in the Survey Laboratory gave the following 

 results : — 



SiOa 

 H2O + 

 CO2 

 K2O 

 Na2 O 

 CaO 



57-90 



Total 



100-07 



It will be seen that the silica percentage is very low; the G0„ 

 percentage is high, and the percentage of alumina is also comparatively 

 high. The presence of potash with a high jtercentage of alumina 

 suggests the occurrence either of felspar or of sericite. The presence 

 of the former is demonstrably present, but the identification of the 

 latter cannot be made with accuracy. From the analysis and the 

 optical characters, the rock would appear to be a talc-chlorite-sericite 

 rock with carbonate crystals, and to be derived from an amphibolite 

 or some closely related tvpe. 



12372, G.M.L. 4320 E. "Ivy" ; consists of fine scales of talc, 

 decomposed chlorite, and granular carbonate ; it closely resembles 

 3391. 



1947 (Old Thunderbolt lease, now G.M.L. 1121 E. Devon Consols 

 Consolidated) is another dark-green chlorite rock, which consists 

 of lenticular areas of talc and carbonate streaked out in parallel 



