ON THE ROCKS OF THE HAURAKI GOLD-FIELDS, 257 



Hypersthene. — In one specimen only, from Kanika Creek, does 

 unaltered rhombic pyroxene occur, where it forms intergrowths 

 with augite. Tn ordinary light it is pale yellowish-brown, but is 

 strongly pleochroic : a pale yellow-brown, /3 darker reddish-brown, 

 y bluish-green. Absorption -y > /3 > a. Cleavage well marked, 

 parallel to 010. Polarization colours rather brilliant. 



Protobastite. — In another specimen, from Waiotahi Creek, proto- 

 bastite occurs instead of hypersthene. It is in rectangular prisms 

 with the prismatic faces but slightly developed. The cleavage is 

 well marked, parallel to 010, and the axial plane is at right angles 

 to it. One transverse section shewed a bisectrix with the axial 

 plane parallel to 100. In ordinary light it is pale yellowish- 

 brown, but is slightly pleochroic ; a pale reddish-brown, /3 yellow- 

 ish-brown, y bluish-green. Absorption y> a > ^. The polariza- 

 tion colours are very brilliant. Remarkably free from inclusions 

 except a little magnetite and apatite, and a few fragments of 

 glass. It is not fibrous and the crystals are sometimes arranged 

 in groups. 



Bastite occurs in all the specimens, except that with proto- 

 bastite. It is in long I'ectangular prisms formed almost entirely 

 by the pinacoidal faces. Cleavage, parallel to 010, is in general 

 well marked. In the specimens from Collarbone Creek it occurs 

 in more or less stellate groups. The axial plane is at right angles 

 to the cleavage. In ordinary light it is pale yellow-brown, but is 

 feebly or rather strongly pleochroic ; a pale yellow-brown, /3 and y 

 bluish-green. The polarization colours are not brilliant. It is an 

 aggregate, but with a distinct maximum extinction parallel to the 

 cleavage. 



Chlorite is found either as a pseudomorph after augite, or else as 

 an infiltration in the ground-mass, or the felspars. It is bluish- 

 green, not at all or faintly pleochroic changing from darker to 

 lighter ; partly isotropic and partly with gray polarization colours. 

 It usually contains minute apatites. In a purple coloured rock 

 from the Karaka, it is bordered with secondary ilmenite, which is 

 often converted into leucoxene on the outer side, while the inner 

 side is not altered. 



Epidote (?) — A little is sometimes seen in the ground-mass or 

 in the felspars, but it is rare, and doubtfully identified. 



Calcite is only abundant in those rocks in which the felspars 

 are decomposed, but it also occurs occasionally in the chlorites. 



Siderite (?) — A brownish, translucent aggregate with the 

 absorption of calcite occurs in some of the bastites in the rock 

 from Collarbone Creek, which may be siderite. 



Quartz (Secondary.) — I have found this in a rock from Karaka 

 Creek. 



K 



