564 JV. L. Bowen — The Binary System. 



Anorthite. 



The optical properties of anorthite (An) had previously 

 been determined in detail at the Geophysical laboratory by H. 

 E. Merwin, and the figures given are the results of his work. 



a = 1-576, y = 1*589, y — a = '013. 2V — 80°±3° 

 = 1-583, G- = 2-765. 



Carnegieite. 



Carnegieite (Cg) always shows polysynthetic twinning simi- 

 lar to that in albite, with high extinction, up to 36°, against 

 the twinning lines. Other Jess persistent twinning lamellse 

 appear crossing these at various angles, often giving a micro- 

 cline-like structure. On account of the universal intricate 

 twinning, many of the optical properties are difficult of deter- 

 mination. The indices, obtained by matching with a liquid in 

 sodium light and determining the index of the liquid on the 

 Abbe refractometer, gave 



y — 1-514, a = 1-509, y-a = '005 



The mean index is therefore low, comparable with that of leu- 

 cite. The birefringence, measured with the compensating 

 quartz wedge, 6 gave *0052 and -0048 in different plates. Opti- 

 cal character negative, 2 V small estimated at 12°-15°, proba- 

 bly triclinic. 



All efforts to obtain euhedral crystals failed. In all charges 

 showing carnegieite and glass (area A D B, Diagram II) the 

 carnegieite is always in rounded crystalline globules. An 

 attempt to grow crystals in a flux gave nothing but similar 

 globules. 



The density of crystalline carnegieite (Cg) is 2'513 at 21°, 

 determined in Thoulet's solution on carefully selected material, 

 free from air bubbles. 



Nephelite. 



In all charges consisting of nephelite and glass (area C B G- 

 F, Diagram II), the nephelite appears under the microscope in 

 perfect hexagonal basal sections, dark with crossed nicols, or 

 rectangular prismatic sections with parallel extinction, indicat- 

 ing the hexagonal nature of these mix-crystals. 



Of the pure sodium compound, nephelite, euhedral crystals 

 were prepared in sodium tungstate over a Bunsen burner. 

 These were in all cases bounded by the prism and terminated 

 only by the base. One of these was measured on the two- 

 circle reflecting goniometer and the hexagonal nature con- 

 firmed. The maximum deviation from 60° of the measured 

 prism angle was 16', and the average deviation 8 ; , with fair to 



