MAGNETITE GARNET KOCKS COULSON. 291 



The garnets are mostly of smaller dimensions (0-07 mm.) than in the preceding 

 No. 245 and they are sometimes enclosed in the magnetite. The larger porphyroblasts 

 of magnetite are confined to certain bands ; they are elongated parallel to the schistosity 

 and contain inclusions of quartz and appear to have a little rutile intergrown with them. 

 Felspar is the most abundant mineral present and it is much altered to an aggregate 

 of micaceous minerals and epidote. Relics of microcline with cross-hatching are 

 present but the greater part of the felspar is a plagioclase of composition between 

 andesine and labradorite. Quartz shows strain polarisation and cataclasis. Biotite is 

 greatly altered to chlorite and secondary magnetite. Muscovite has also been 

 developed from biotite and is not symmetrically disposed to the schistosity planes. A 

 little bleached biotite and accessory apatite occur. Granoblastic, porphyroblastic, and 

 cataclastic structures are the chief ones present. The rock is a Garnet-Magnetite-Schist. 



No. 102. This is a massive type with dominating garnet. Most of it is fine 

 grained but in parts the crystals of garnet and quartz attain considerable size. 



Garnets form 40-8 per cent, of the rock and occur as irregular masses traversed 

 by numerous cracks along which iron ore occurs (Plate II, fig. 5.) When the garnet is 

 altered to chlorite, a larger amount of iron ore is developed. Garnet is also intergrown 

 with magnetite and quartz ; and all three minerals contain inclusions of one another. 

 Limonite is present as a pseudomorph after magnetite and there is a fair amount of 

 rutile intergrown with the magnetite ; this is red by reflected light and probably absorbs 

 the 1-14 per cent, of TiO 2 , in the rock. Apatite is more abundant than usual and occurs 

 chiefly with the magnetite. Quartz is abundant and contains numerous inclusions of 

 minute iron ore individuals arranged in parallel lines. A few zircon crystals occur. 

 The structure is diablastic and the texture is massive. It is Garnet-Quartz-Magnetite 

 Rock. 



No. 348. This is a schistose variety with bands of minute pink garnets and clear 

 quartz, which show up well from the otherwise greenish-black rock. Scattered through 

 the rock are occasional porphyroblasts of magnetite and in this respect the specimen 

 resembles Nos. 181 and 288. 



Garnets are numerous and form one-fifth of the rock but the average size of the 

 grains is only 0-06 mm. The chemical analysis shows that this rock contains 8-23 per 

 cent, of MnO and it is probable that this is contained in the garnet. Magnetite occurs 

 both as xenoblastic and idioblastic individuals which generally have their longer axes 

 parallel to the schistosity. Felspar and quartz are present in equal proportions. The 

 felspars are almost entirely kaolinised and their original nature is somewhat indefinite ; 

 such extinction angles as are measurable indicate andesine but orthoclase is also present. 

 Quartz contains gaseous, garnet, and magnetite inclusions and shows strain polarisation. 

 Green biotite is commonly altered to chlorite. Epidote and calcite, both probably 

 derived from the alteration of the felspars, as well as apatite and zircon, are present. 

 The structure is both porphyroblastic and granoblastic and the rock is a Garnet-Magnetite- 

 Schist. 



