BY D. MAWSON. 



589 



approximated to by any of the analyses quoted. In all cases a 

 considerable amount of ferrous iron is returned, as also are 

 varying quantities of the other protoxide bases. No strict 

 analogy was found amongst any of them when stated in group- 

 ings of like vicarious constituents. 



Petrological features. — A slide prepared from the remaining 

 part of a crystal, portion of which, on analysis, had returned no 

 ferrous iron, showed it to be of a bright grass-green colour by 

 transmitted light; pleochroism along a horizontal axis, slightly 

 yellower than that along a(near c); extinction with c = 3°. The 

 mineral is therefore rather a bright green variety of aegirine. 



The crystals are often much zoned, especially in the smaller 

 veins; a single individual may show a succession of stages inter- 

 mediate between segirine-augite and *girine(see textfig.l). 



Fig. 1. — Zoned pyroxene; segirine-augite within to segirine externally. 



Such progressive change in optical properties from the kernel 

 outwards is evidently occasioned by a systematic development of 

 its molecular constituents, whereby protoxide bases, most 

 abundant in its earlier stages of growth, were later on replaced 

 in increasing amount by sesquioxides; also that the earlier 

 crystallisations were marked by greater abundance of lime, 

 magnesia and like molecules in place of iron. 



