OCCURRENCE OF TINGUAITE AT KOSCIUSKO, N.S.W. 349 



Rosenbusch has described, in his magnificent work, 1 a variety 

 of nepheline rock, which he refers to the basic group, from the 

 Katzenbuckel, a dome shaped hill in the Odenwald, Baden. He 

 terms this rock phonolitic nephelinite. In many respects it very 

 closely resembles the Kosciusko nepheline rock, but the Katzen- 

 buckel rock contains some olivine together with abundant hauyne, 

 whereas these two minerals are wanting in the Kosciusko rock. 



Professor Brogger has described nepheline rocks which though 

 not definitely phonolites, are nevertheless as regards chemica 

 composition, so closely allied to the Kosciusko rock, that they 

 may be quoted here for comparison. 



The rock described by him under the section of laurdalite from 

 Lunde, Lougenthal, in the Christiania district is shown by its 

 chemical composition to be not far removed from the nepheline rock 

 of Kosciusko. A comparison however, of its chemical composition 

 with that of the Kosciusko rock shows that the laurdalite is richer 

 in lime than that of Kosciusko and correspondingly poorer in soda. 

 Mineralogically it differs from the Kosciusko rock chiefly in 

 having phenocrysts developed of potash felspar belonging to the 

 varieties sanidine and orthoclase. In other respects, however, its 

 minerals agree very closely with those developed in the Kosciusko 

 rock. 



The same author has described under the term nepheline- 

 porphyry, also from the Lougenthal, a rock both chemically and 

 mineralogically intimately related to that of Kosciusko. This 

 nepheline-porphyry is richer in soda than the laurdalite, containing 

 11*36% of soda as compared with 8*18% in the latter. This 

 alumina per centage in nepheline-porphyry is higher than that in 

 the Kosciusko nepheline rock, and mineralogically it differs from 

 the Kosciusko rock chiefly in having potash felspar developed 

 as phenocrysts. The rock termed tinguaite, described by him 

 from Hedrum, lithologically very closely resembles the Kosciusko 

 rock. 



1 Mieroscopische Physiographie der Mineralien und Gesteine, dritte 

 Auflage, Vol. n., p. 1260. 



