SCHAIiLBR.] 



Spodumene from Sun Diego County. 



269 



much larger than the other two. The crystal thus presents a 

 tabular appearan ce . 



The orthopinacoid is rather frequently present, though 

 occasionally it is very narrow and rounded to such an extent as 

 to render it difficult to definitely decide if it be present or not. 

 Then again, it may be very broad making the crystal tabular. 

 A marked feature of the orthopinacoid is that it is always deeply 

 furrowed vertically. 



The clinopinacoid is not of frequent occurrence, though it 

 has been noted a number of times, from a narrow face, less than 

 a millimeter wide to one almost a centimeter in width. Fig. 2, 

 Plate 26, shows the crystal having the broadest clinopinacoid. 

 'Prom left to right the faces in the prism zone, on this crystal, 

 are (130) (very narrow) , (OlO), (llO), (100) (furrowed). The 

 orthopinacoidal faces are the only ones striated. 



Habit. — Three habits are noticed in these crystals, depending 

 on the relative size of the faces in the prismatic zone. 



The most common habit and the one that is more or less 

 confined to the smaller crystals, is a tabular form resulting from 

 the inequality in size of the prism faces. Other faces, such as 

 the pinacoids are usually absent from crystals of this type. 



The second most frequent type is where the orthopinacoid is 

 very large and the crystals become tabular parallel to this form. 

 This habit seems to be restricted to the larger crystals. 



In the third habit, all three forms, the prism and the two 

 pinacoids are equally developed and the crystal becomes octago- 

 nal in shape. This habit is of rare occurence. 



Plate 26 is a photograph of seven crystals. Crystal 6 has the 

 first habit, crystals 4 and 7 have the second habit, and crystal 2 

 has the third habit. 



ETCH FIGURES. 



On the Unit Prism. — A very marked feature of these crystals 

 is the profusion of natural etch figures which thickly crowd all 

 of the natural faces of the crystals, except the orthopinacoid. 

 Even cleavage (prismatic) pieces frequently show them. 



On the faces of the unit prism they are especially thick as can 

 be seen in Fig. 6, Plate 26, which is a crystal tabular to a prism 



