226 PHYSIOGRAPHY. CLASS II. 



lite. Man. p. 142. Sodalite. PHILL. p. 127- Sodalit. 

 HAUSM. II. S. 524. Sodalit. LEONH. S. 457. Soda- 

 lite. HA Y. Traite; 2de Ed. T. III. p. 59. 



Fundamental form. Hexahedron. Vol. I. Fig. 1. 

 Simple forms. H; D, Vol.1. Fig. 51. Vesu- 

 vius. Combination. 1. H. D. Fig. 151, the 

 faces of the hexahedron very small. Greenland. 



Cleavage, dodecahedron perfect. Fracture con- 

 choidal, uneven. Surface smooth, sometimes 

 rather uneven. 



Lustre vitreous. Colour green, greenish-white, 

 passing into greyish- and snow-white. Streak 

 white. Translucent. 



Brittle. Hardness = 5-5 ... 6'0. Sp. Gr. = 2-295, 

 crystals from Greenland. 



Compound Varieties. Massive : composition 

 granular ; faces of composition uneven. 



OBSERVATIONS. 



1. Two analyses of the present species, one by ECKE- 

 BERG, another by THOMSON, have yielded 



Silica 36-00 38-52. 



Alumina 32-00 27-48. 



Lime 0-00 2-10. 



Oxide of Iron 0-15 1-00. 



Soda, and a little Potash 25-00 23-50. 



Muriatic Acid 6-75 3-00. 



Volatile substances 0-00 2-10. 



Its chemical formula is Na 3 'Si 2 + 4 Al Si, which corres- 

 ponds to 27-62 of soda, 30-25 alumina, and 42-13 silica. 

 Before the blowpipe it melts, with intumescence and de- 

 velopement of air bubbles, into a colourless glassy globule : 

 with borax it melts difficultly, but only if added in a small 



