The ferro-magnesian silicates are subordinate to the felspars ^ 

 are usually oligoclase to labradorite. 8oda attains its max 

 of 3 to 5 per cent. Quartz is often present in the holocryst 

 rocks, but in the semicrystalline rocks it is usually absorbec 

 the base. S.G. 2-55 to 2'85. 



with a little quartz. The plagio- 

 clase is either in broad plates or in broad laths. 



BlOTITE DiORITE. 



Lower Buller Gorge.— A medium grained dark grey rock shew- 

 ing wliite triclinia felspar and quartz with abundance of biotite 

 and hornblende. S.G. 2-89. Section : Quartz is tolerably 

 abundant in allotriomorphic crystals from -01 to "06 in diameter, 

 and contains rather large fluid cavities. The felspars are broad, 

 the length about twice the breadth, and are well twinned ; they 

 are from -02 to -07 in length. The hornblende is brown, chiefly 

 allotriomorphic and up to -05 in length. Biotite is more abundant 

 tlian hornblende and in crystals up to -08 in diameter. There is 

 a little apatite and blue-green chlorite. Occurs as a dyke in 

 gianite, close to the bridge over the Ohika Creek. 



HORNBLEXDE DiORITE. 



Upper Buller District — Medium grained, black and white 

 speckled i-ocks, composed of white felspar and black hornblende. 

 S.G. 2-81 to 2-9. Section : The felspars are much altered, but 

 polysynthetic twinning is sometimes plain in rather broad bands ; 

 the crystals from -02 to -08 in length. The hornblende is chiefly 

 allotriomorphic, from -025 to -08 in length. In ordinary light it 

 is yellowish-green, but is pleochroic changing from pale yellow- 

 green to deep bluish-green. There is also some magnetite. 

 Secondary minerals are quartz and chlorite. In some specimens 

 there is very little felspar, and that is in allotriomorphic grains. 

 Schis 



prisms Ivmu' in tlie 'pl'uie schistositV. The felspar i« i" ^^^^^"^ 

 grains vvlii,|, ^h.-w brilliant; pularization colours like quartz, but 

 the L;i;iins .nc soincTinu's cUaN til, often partly decomposed, and 

 occasinnally sli.-w pnl ysyni hrti,- twinning. Known only as boulders 



Enstatite Diohite, 



Bluff mil, Southlami—A. tine to medium grained, granular 



rock, speckled black and white, in nearly equal parts. S.G. 2-88. 



