140 



Mr. W. J. Lewis's Crystallograplric Notes. 



Quercite. — The crystallography of Quercite has been already 

 determined by Senarmont (Rammelsberg's Die neuesten For- 

 schungen in der Kry stall- Chemie) ; but it was a matter of 

 interest to determine whether any difference either in habit or 

 angles could be found in the crystals obtained from the new 

 source. The crystals were found to show the same hemimor- 

 phous habit (fig. 1) observed by Senarmont ; and but a slight 

 change has been made in the elements, which may probably 

 be explained by the fact that the crystals obtained by Dr. 

 Miiller were very perfect. 



The crystal is positive ; the optic axes lie in the plane of 

 symmetry ; the mean line lies between c and g, and makes 

 an angle of about 20° with the normal to g, the dispersion 

 (incline'e) being considerable, v > p. The angles of the optic 

 axes in air for the red and blue rays were found to be 55° 17' 

 and 58° 20^ respectively. 



Fig. 1. Fig. 2. 



The forms observed are a{l 0}, m {1 1 0}, c {0 l},/{0 1 1}, 

 g{l 1} (fig. 2). The faces of the prism are striated parallel 

 to their intersection with a ; and there is a good cleavage 

 parallel to g { 1 1 } . The following are the elements and prin- 

 cipal angles observed and calculated. 



(1 0, 1 1) = 35° 32 / «2, (1 1, 1) = 33° 30'-8, 

 (010, 111) = 66°1 / . 



a: b: c=l : 1-241 : 0*95. 





Calculated. 

 ■ 



Observed. 



Senarmont. 



A 





Calculated. 



Observed. 



a c 



c 9 



^9 a j 



*69 3 

 53 201 

 *57 36f 



69 5 

 53 161 

 57 35 



6$ 57 



68 57 



53 22 about 



57 20 



Iff, 



*35 33J> 

 108 53 



35 32 

 108 49J 



35 34 

 108 52 



35 32 

 109 5 



