COMPOSITION OF N.S.W. LABRADORITE AND TOPAZES. 193 



On the COMPOSITION of N. S. WALES LABRADORITE 



and TOPAZES with a COMPARISON of METHODS 



for the ESTIMATION of FLUORINE. 



By G. Harker, b Sc. 



(Communicated by Professor Liversidge, m.a., ll.d., f.r.s.) 



[Read before the Royal Society of N. 8. Wales, December 6, 189'J.~] 



Analysis of Mineral Labkadorite from N. S. Wales. 



The specimen described in the following note was collected by 

 Mr. D. A. Porter of Tamworth on Sandilands Mountain, some 

 fifty seven miles from Tenterfield, who forwarded it to Professor 

 Liversidge for examination. Mr. Porter states that it occurs 

 there in a basalt and also between Hillgrove and Grafton. 



The specimens were in broken fragments about half an inch in 

 diameter. Some were colourless, others brown to greyish. One 

 perfect cleavage was exhibited, probably basal, and a second not 

 quite so good. The fracture was uneven inclining to conchoidal; 

 the lustre vitreous. The hardness was 6 and the specific gravity 

 2*70. Before the blowpipe it fused to a colourless glass, its 

 fusibility being about three. All these properties agree in every 

 detail with those given in Dana for typical labradorite, as do all 

 the optical properties which were determined. The refractive 

 index was low and the double refraction weak. In convergent 

 polarised light a cleavage flake gave a figure with one brush nearly 

 straight and was therefore the section of a bi-axial mineral cut at 

 right angles to the optic axis, the optic axes being nearly at right 

 angles. The dispersion could not be obtained. The mineral was 

 optically positive and shewed multiple twinning. 



Analysis. 

 1 2 



New South Wales. 



Silica 55-05 54-81 



Alumina ... Ioa.ik J 29*70 

 Ferric oxide ... J { -42 



3 



Veltliu. 



55-15 

 29-15 



4 



Thaiinbergthal. 



53-61 



2968 



5 



Rameiii-Brod. 



54-55 



28-68 

 1-03 



M— Dec. 6, 1899. 









