74 JACUPIIIAXGITK rX TASMANIA. 



Stanley Jevons includes it in the family of ij elites (pyroxene- 

 felspathoid rocks), presumably owing to its mineral coi»- 

 position. As a rule, however, ijolites are much poorer in 

 titanic acid and iron than jacupirangite. 



At Port Cygnet the rock cannot be called a geological 

 entity. It does noit occur as a dyke of later material in- 

 vading the main mass of syenite. It may rather be inter- 

 preted as resulting from differentiation by progressive cry- 

 stallisation, the marginal parts of the cooling mass receiving 

 concentrations of basic oxides, while the centre was left 

 more acid. The minor variations are interesting; thus, 

 vein-like bands of elaeolilte syenite may be seen ramifying 

 in the jacupirangite, and the latter also' occurs as segregation 

 spots enclosed in the lighter coloured rock. The central 

 portion of the magma naturally consolidated after the cool- 

 ing of the periphery. 



The concentrations of iron ore into which the Brazilian 

 rock merges have not been noticed at Port Cygnet; in fact, 

 our rock is not at all rich in magnetite or ilmenite. The 

 augite, too, is evidently not titanic. The titanium in the 

 rock would appear to principally reside in the sphene. 



