Waring — Quartz from San Diego County, California. 125 



xAjrt. XVI. — Quartz from San Diego County, California;* 

 by G. A. Waring, Stanford University, California. 



In quartz crystals occurring in the pockets of the gem-bear- 

 ing pegmatite veins of the Pala and Bincon districts, San 

 Diego County, California, several peculiarities of crystallization 

 have been observed, which it is believed have not before been 

 described. These crystals occur attached to the sides of the 

 cavities, associated usually with albite and orthoclase. The 

 most remarkable feature about them is the common develop- 

 ment of tetartohedral faces. 



On two crystals, figs. 3 and 7, the facial angles were measured 

 by means of a Fuess reflecting goniometer, and the following 

 rare faces determined, according to Bravais-Miller system of 

 notation. 



On the small crystal, fig. 



m A r (4041) 

 rii/^x (5161) 



On the crystal, fig. 3 :— 

 m^x (5161) 

 m^y (41 o 1 ) 



m^s (1121) 



The r (±011) and M (3031) faces also are present on this 

 crystal, determined by measurement with the contact goni- 

 ometer, and the w-face (314:1) is also developed ; it is distinctly 

 visible with the pocket-lens, but too small to be measured with 

 certainty. It has the terminal pyramids partly developed at 

 the other end also, and imperfectly showing the rare faces. It 

 is intergrown with a left-handed crystal which on the face 

 preserved exhibits the faces s (2111), x (6151) and Y (±04:1). 



Twinning is common and, so far as observed, is always 

 according to the Dauphine law. The upper part of the crys- 

 tal shown in fio\ 3 is such a twin, of two right-handed indi- 

 viduals very perfectly joined, the twinning plane but faintly 

 shown by cloudy patches within the crystal. 



Fig. 1 is a twin of two left-handed individuals, the plane of 

 twinning being well marked on the surface by a discontinuity 

 in the prismatic striations, and by a plane of dark patches 



* Sincere appreciation is expressed to Dr. M. Murgoci of Vienna for 

 assistance in the measurement of the inter-facial angles, and to Dr. J. P. 

 Smith of Stanford University for advice and aid in the preparation of this 

 article. 



i . — 



Measured. 



Given by Dana 



11° 



12' 



11° 8' 



11° 



50' 



12° 1' 



Measi 



ired. 



Given by Dana 



11° 



27' 



12°* 1' 



14° 



8' 





14° 



54' 



14° 35' 



14° 



10' 





37° 



39' 



37° 58' 



