115 



Uralite, such as described above, is present in most of 

 the rocks of the main intrusion. In the "yatalite" pegma- 

 tite in these rocks it occurs in very large subidiomorphic crys- 

 tals up to 2 in. in length. It is an actinolite of a very deep 

 green, and includes poikilitically much titaniferous magne- 

 tite sphene quartz, and smaller uralite grains of different 

 orientation. Primary hornblende may also be present. 

 There is no doubt but that the actinolite crystals are ural- 

 itic from their mode of occurrence and their pyroxenic cleav- 

 age net, when viewed in basal section ; moreover, they contain 

 residual patches of unaltered diopside, almost colourless, and 

 of a higher extinction angle. By weathering, the uralite 

 has given rise to the formation of limonite, which frequently 

 greatly obscures the crystals. 



Primary hornblende occurs, however, both in the ''yata- 

 lite" and in a few of the specimens examined of the main 

 rockmass. It is easily distinguished from the secondary 

 amphibole by its brown colour, stronger pleochroism, and 

 clear amphibolitic cleavage net. Though generally allotrio- 

 morphic, subidiomorphic crystals appear, and sometimes per- 

 fect six-sided basal sections are observable. In only one rock 

 is it a notable constituent, occupying about 12 per cent, of 

 the area of the section. 



Biotite is rare among rocks of the main intrusion, though 

 appearing along its western margin. It is in its usual flaky 

 form, the plates being roughly parallel to the banding of 

 the rock. The pleochroism is normal, frequently obscured 

 by partial chloritization, accompanied by a separation of iron 

 oxides, magnetite, and limonite. In one section taken from 

 the eastern vein on the Gumeracha Road biotite occurs in 

 small amount in the cleavage plates of the uralite. 



Titaniferous iron occurs in a varying but generally an 

 unusually large amount. Chemically it varies from an ilmen- 

 ite, which, though containing a good deal of Fej Og, is very 

 insoluble in acids, to a magnetite strongly attracted by a 

 magnet, but in which titanium is shown to be present by the 

 formation of leucoxene and the faint violet colour given in 

 reduction tests. Such titaniferous magnetite occurs in the 

 variety of pegmatite found in these rocks, forming there large 

 subidiomorphic crystals 2 in. in length, and irregular grains 

 included poikilitically in the uralite. In the main body of 

 the rock it occurs in composition more nearly that of theoreti- 

 cal ilmenite, in crystalline plates roughly idiomorphic, or in 

 irregular masses, but in all cases with the longer axes parallel 

 to the banding of the rock. Where banding is marked ilmen- 

 ite is generally segregated into bands. The mode of altera- 

 tion into leucoxene or titanomorphite is quite normal. 



