460 Sterrett — Tourmaline from San Diego County, Gal. 



Many crystals are of gem quality, and according to " The 

 Mineral Industry,"* $15,000 worth of gems were produced 

 from this locality during the year 1901, and Mr. Schernikow 

 places the value for 1903 between $40,000 and $50,000. . 



The number of forms found on the crystals is not great and 

 only those common to tourmaline have been observed, a list of 

 which is given in the accompanying table and shown in stereo- 

 graphic projection in fig. 1. 



Prisms. 

 a (1120) 

 m (1010) 



771,(0110) 



<r (1230) 

 h (1450) 



Upper end. 

 C (0001) 

 r (1011) 

 O (0221) 

 t (2131) 

 x (1232) 



Lower end. 

 c' (0001) 

 / (0111) 

 e' (1012) 



The forms a and A could not be accurately 

 determined, for the prism faces of the crys- 

 tal on which they were measured were badly 

 striated. Reflections were obtained from thin 

 glass strips glued on these faces, and gave 

 results approximating to the above symbols. 

 The character of the other crystals measured 

 was such as to permit very satisfactory deter- 

 minations of the forms enumerated, but it 

 has not seemed necessary to publish a list of 

 the angles measured. 



Although owing to the hemimorphic char- 

 acter of tourmaline, the three r faces above 

 form a triangular pyramid and not, strictly 

 speaking, a rhombohedron, it will be con- 

 venient to refer to this and similar forms as 

 rhombohedrons, and for like reason to call 

 the t and x faces scalenohedrons. 



All of the figures drawn in clinographic 

 projection have the antilogous end up, i. e., 

 that pole which on cooling is positively elec- 

 trified, and when tested by the Kundt method 

 attracts sulphur. The crystals all follow the 

 general rule, that the end with the steeper 

 forms is the antilogous pole. 



For a single locality the crystals show an unusual diversity 

 of habit and color, and in describing them it will be convenient 

 to divide them into types. In the first type the rhombohedron 

 o forms the principal termination above, sometimes with a 

 replacement of its edges by ?', as shown in fig. 2. The lower 



* Published by the Engineering and Mining Journal of New York. 



a 



Mi 



