102 



FllYSIOGllAl'IlY. 



Colour white. Transparent. Index of refraction 

 = 147 (that of the Wavellite being = 1-52), 



WOLLASTON. 



It occurs in minute crystals affecting the form of the 

 fundamental pyramid, with its most acute solid-angle re- 

 placed, along with the Wavellite from Cornwall, and was 

 discovered by LEVY, but named and examined by WOL- 

 LASTON, who found it to contain alumina and fluoric acid. 



FORSTERITE. 

 GEM. 



Forsterite. LEVY. Ann. of Phil. XXXVII. p. 61. 



Prismatic. Combination observed similar to Fig. 28, 

 without z and P. Inclination of M on M = 

 128 54'; of y on y (over M) = 107 48'; y on 

 y (adjacent) = 139 14'. 



Cleavage easy parallel to o. 



Colourless, brilliant, translucent. 



Hard enough to scratch quartz. 



It contains, according to Mr CHILDREN, silica and mag- 

 nesia. It was discovered by Mr LEVY in small crystals, 

 accompanying pleonaste and olive-green pyroxene on Mount 

 Vesuvius. The angles of this substance agree pretty nearly 

 with those of prismatic Corundum, given Vol. II. p. 304., 

 in the same succession = 128 35', 107 29', and 139 53', 

 only the face perpendicular to the axis, which in Forsterite 

 has even an easy cleavage parallel to it, has not yet been 

 observed in prismatic Corundum. 



GEHLENITE. 

 SPAR. 



Gehlenite. JAM. Syst. Vol. I. p. 138. and Vol. III. p. 536. 

 Man. p. 323. Gehlenite. FHILL. p. 35. 



