232 



to a compact hornblende, strongly pleochroic but of pale 

 colour, and partly to actinolite. A further change to blue- 

 green chlorite is in progress. Ilmenite is very abundant, pass- 

 ing into leucoxene. 



Another specimen labelled "5 miles west of Blinman"^ 

 is of very similar texture. The felspar, as before, is pro- 

 bably oligoclase, and is largely altered to yellow epidote. 

 Where this rock differs from all others is in the presence 

 in it of much scapolite of comparatively low double refrac- 

 tion. In a slide, certainly unusually thin, the colours shown 

 are rarely above the first order. The mode of occurrence, 

 cleavage, refractive index, and optically negative character 

 all point to its being scapolite. It is probably a variety of 

 mizzonite. The alteration of the augite is chiefly to a com- 

 pact pale-green or brown hornblende, with dark chloritic 

 border. Actinolite is less common. Sphene occurs, but in 

 such an association with ilmenite that it is probably titano- 

 morphite. Ilmenite with leucoxene is rather plentiful. 



GABBRO-DIABASES . 



These are rocks of such coarse grain and allotriomorphic 

 gabbroid structure that they seem to be intermediate be- 

 tween gabbros and diabases. 



Natne. — Granophyric quartz gabbro-diabase. 



A specimen labelled 'Dyke, west of gneiss, 1 mile west 

 of Blinman" is best described as a granophyric quartz gabbro- 

 diabase. Magnetite was the first mineral to crystallize, and 

 following this felspar and augite crystallized apparently con- 

 temporaneously. This left angular spaces filled with a 

 (probably) entectic mixture of quartz and felspar, which 

 solidified in a granophyric intergrowth. (See microphoto- 

 graph, fig. 3, pi. xv.) The felspar is completely altered to 

 exceedingly fine saussurite, faintly pleochroic, and with little 

 or no sign of original twinning. The expansion of the fer- 

 romagnesian minerals on alteration to chlorite has cracked 

 the saussurite, and chlorite has formed in these cracks. The 

 pyroxene of the original rock may have been diallage, as 

 several minor features suggest. It is now, however, entirely 

 converted to uralite (smaragdite), and on the periphery of 

 the grains this has become clinochlore, with the separation 

 of magnetite, in part hydrated to a dusty limonite. A little 

 pistacite is also present in the felspar, uralite, or in the 

 chlorite-filled crevices. In the angular spaces between the 

 felspar and pyroxene crystals granophyric quartz and felspar 

 occur, the latter having the lower refractive index. Free 



