Vol. 65.] AND MAGNESIAN ROCKS OP NEW ZEALAND. 



373 



No. 



299 [12, vol. ii, p. 



151]. 







! Glaucophane 

 1 (AlNaSi 2 G ). 



Eiebeckite , r ,., 

 R 2 m (Si0 3 ) 3 . ^ e P hnte - 



Abstract. 



Si0 2 



56-41 

 091 

 3-84 

 1-92 

 0-15 

 19-09 

 12-81 

 2-64 

 2-56 



2-14 

 0-91 



055 



5-76 I 48-51 



3-84 ...... 



1-92 



: 0-15 



1909 



12-81 



1-49 : 0-60 

 1-15 



Nephrite 84-23 



Glaucophane ... 3*60 



Eiebeckite 11*09 



excess H^O ... 1'41 



A1 2 3 



Fe„0 3 



FeO 



MnO 



MgO 



100-33 



CaO 



Na,0 



H 2 





Total ... 



100-33 



3-60 



11-09 84-23 



! 









Microscopic characters. — It is noteworthy that nearly all 

 the minor differences in colour and structure by which hand-speci- 

 mens are distinguished, disappear almost entirely when sections are 

 examined under the microscope. The mineral aggregate is practi- 

 cally colourless, and non-pleochroic. The structure shows up to 

 most advantage under high powers and between crossed nicols. It 

 is then seen to consist of a dense mass of extremely fine amphibole- 

 fibres, closely interlocked, and either roughly foliated, or arranged 

 in sheaves, tufts, and radiating groups ; but throughout the rock 

 a more or less banded or foliated structure is evident, indicating 

 considerable pressure and movement (PI. XVI, fig. 4). The fibres 

 are so highly twisted and felted that it becomes difficult to measure 

 extinction-angles. When the extinction can be observed, it is very 

 often straight; but it varies fromO° to 20°, the highest measured angle 

 being approximately 20°. This was the angle for New Zealand 

 nephrite observed by Dr. Clarke & Prof. Merrill [11]. Prof. Iddings 

 obtained 15° as his highest angle [12, p. 85], while the angles for 

 related species recorded by other authorities are as follows : — 



J. D. Dana, ' System of Mineralogy ' 6th ed. (1892) p. 389, 15° (actinolite). 

 C. Hintzb, ' Handbuch der Mineralogie ' vol. ii (1897) p. 1188, 16°-18° 30' 



(non-aluminous hornblende). 

 A. M. Levy & A. Lacroix, ' Les Mineraux des Roches ' 1888, p. 144, 15°. 



Of accessory minerals, epidote appears to be present in pale- 

 yellow or colourless granules and needles of extreme fineness. 

 Magnetite is frequently present in small grains. Chromite is only 

 an occasional accessory, but there appears to be another spinel pre- 

 sent in small brown grains : this is probably picotite. Lastly, small 

 granular garnets occur, colourless to pale brown. Dr. Dieseldorff 

 records epidote and garnet in specimens from D'Urville Island [5, 

 pp. 340 et seqq.~\, a locality which I was unable to visit or to collect 



Q. J. G. S. No. 259. 2 c 



