17 



On some so-galled South Australian Rubies. 



By Professor E. H. Rexnie, D.Sc. 



[Read May 1st, 1888.] 



As is well known, considerable controversy has arisen in Ade- 

 laide as to the nature of the red stones recently found in large 

 quantities in the northern interior of South Australia, some 

 stating that these stones are genuine rubies, others that they are 

 spinelles, others that they are garnets, while others still imagine 

 that they are something quite new. The latter notion has arisen 

 chiefly, I think, from statements made that they are infusible and 

 harder than garnets, though scarcely hard enough for rubies. It 

 has often occurred to me that it is somewhat strange that so far 

 no results of any chemical examination of these stones have been 

 published, such an examination being, in my opinion, the crucial 

 test of their nature. By the courtesy of various gentlemen some 

 of these stones from three of the Companies, viz., McDonnell 

 Ranges, Hale River, and Maude, have lately been placed at my 

 disposal. Before stating the results obtained it may be well to 

 state briefly the nature of the various minerals above alluded to, 

 viz., rubies, spinelles, and garnets, and to show that they diifer 

 widely from one another in chemical composition. 



1. Rubies. — These consist essentially of alumina, but there may 

 be present small quantities of impurities, especially magnesia and 

 silica. 



2. Spinelles. — These consist essentially of an aluminate of 

 magnesia, but there may be present, according to Dana, from 

 about 1^ to 5|- per cent, of silica, with occasionally considerable 

 quantities of lime and oxide of iron. 



3. Garnets. — These vary greatly in composition, but are in all 

 cases silicates. I have only been able to find two cases in which 

 the silica is below 35 per cent., and in those cases the percentages 

 are about 34 and 31 respectively. They may be silicates of lime and 

 alumina, of iron and alumina, of magnesia and alumina, of man- 

 ganese and alumina, of lime and iron, of lime and chromium, 

 with varying small quantities of other constituents. 



To come now to the results of analysis. All the specimens I 

 have examined have proved to be silicates of alumina and iron, 

 with small quantities of oxide of manganese, lime, and magnesia, 

 and hence are undoubtedly garnets, as Mr. Streeter says, " of the 

 Almandine variety." The following are the quantitative results 

 obtained by the analysis of some of the stones from tlie Halo 

 River : — 



