594 MINERALS AND VEINS OF ^EGIRINE-SYENITE, 



Refractive index not measurable directly by the refractometer; 

 mean value determined with oils about 1-66. Birefringence, 

 very weak and positive. 



Dispersion very great. Optic orientation with sodium light, 

 extinction angle on b, sAc = 6° in front. No complete extinc- 

 tion in sunlight, due to marked dispersion of the optic axes. 



Fusibility does not exceed 2, the fused mineral forming a black 

 magnetic globule. Very little affected by considerable digestion 

 on the water bath with concentrated HC1 or H 2 S0 4 . 



Result of Analysis. — Specific Gravity 3"35. 



Molec. Ratio. 



SiO, *.. 



. 48-90 



0-815 



Ti0 2 



. 0-65 



0-008 



A1 2 3 



trace 





Fe 2 3 



. 8-70 



0-054 



FeO 



. 26-76 



0-372 



MnO 



1-09 



0-015 



CaO 



. 1-35 



0-024 



MgO 



Na 2 



. 0-20 

 . 8-53 



0-005 



0-138 



E 2 



. 1-60 



0-017 



Li 2 



. 0-60 



0-020 



H. 2 O + (110°C.) 

 H a O-(110°C.) 

 Fl 



1-67 

 . 0-29 



. o-is 



0-092 



Zr0 2 



trace 





Cl.S0 8 .P B B .6r a 8 . 



v 2 o s .co 2 ... 



| nil 





100-52 



Less equivalent of Fl -08 





}c 



S23-h0-052=15-S3 

 0-054 =1-04 



0-416 =8-00 



0-267 =5-13 



100-44 



Notes on the Analyses. — -Several methods for separating the 

 pure mineral were tried, until finally it was found necessary to 

 hand-pick the crushed veinstuff, each crystal fragment then being 

 separately tested by observing its streak when crushed in an 

 agate mortar; in this way, the arfvedsonite was distinguished 

 from all other associated dark minerals, and by rejecting any 



