ON GLAÜCOPHANE. 87 



II. Clinopinacoidal Section. 



As the glaucopliane-inclividuals are all more or less arranged 

 parallel with the orthopinacoid, to the plane of a schistose structure of 

 the rock, slides taken in the longitudinal direction of the schist present 

 quite a different aspect; here the crystals show all a liglit green with 

 a slight tinge of blue. The sections are slender, and terminate in 

 sharp points at both ends with unsymmetrical sides, thus indicating 

 the probable presence of one of orthodomes. The surface of the section 

 taken parallel to the clinopinacoid shows usually a striated appearance, 

 while only a few stripes, if ever present, have been observed on the 

 orthopinacoid. This is, indeed, a very characteristic feature. The 

 direction of extinction : — c : C= 11° — 12°; these figures* seem to be 

 somewhat large in comparison with those already well known to us. 



III. Orthopinacoidal Section. 



The section in this direction presents a broad tabular form with- 

 out any distinct termination at both ends, being often resolved more 

 or less into radiating fibres, so this particular feature gives a clue as to 

 the direction in which a section is taken. 



Various tinges of colour are discernible even in the same in- 

 dividual; the central part is lighter in tinge and more purple in its 

 hue, while the periphery is intensely coloured, and a shade of green 

 predominates. This zonal arrangement has also been observed by 

 Stelzner f in the Swiss glaucophane, and G. H. Williams J assigned 

 the cause to the new formation of arfvedsonite from glaucophane. 



* c:C = 3°- 4° as is observed by Luedecke ia the specimen from Syra iu Greece : Zeitschrift. 

 d. deutch. {,'eol. Ges. 1876, XXVIII, p. 249. Vide also Tschermnk's Mineralogische u. pet:ogra- 

 phische Mittheilungen, 1879, II, p. 71. 



t Neues Jahrbuch für Mineralogie etc., 1883, I Band, p. 209. 



Î ibid. 1882, II Band, p. 202. 



