Sterrett — Tourmaline from San Diego County, Col. 463 



parent and clear. One crystal lias a lilac-colored band, formed 

 by the blending of pale blue and pink layers. 



Crystals of a fourth type are often short 

 and stout, terminated by basal planes and 

 rhombohedrons. The prism zone is made up 

 of deeply striated faces ; or more properly 

 speaking, layers of smalt crystals. The termi- 

 nations consist of the bases and rhombohe- 

 drons, <9, r, t\ and e' ' . The termination at 

 the antilogous pole more often fails, and is 

 generally rough and much corroded. Fig. 8 

 is a basal projection of the analogous pole 

 of a distorted crystal of this type. These crystals commonly 

 have a pink or white middle and green layers or cap at 

 the ends. The corroded end is a dark semi-transparent green ; 

 while the other is transparent grass- or pale apple-green. One 

 crystal has a cap of pale sulphur-yellow color. Other excep- 

 tions are white crystals, faintly tinted with pink and contain- 

 ing perfectly colorless portions. 



Crystals of a fifth type have a black exterior or shell ; gen- 

 erally less than a millimeter thick. Within there is a core of 

 light colored material, green, pink or whitish. When the termi- 

 nations are present, they are found to be <?, o and r above with 

 c' and r' below. 



11 



All of the crystals with an olive- or pistache-green color are 

 included in a sixth type. Some are slender, as No. 1 of the 

 plate ; these are olive-green passing into brownish green at the 

 upper end. Others vary up to 5 cm in thickness and often have 

 a silky luster with pistache-green color. The upper termina- 

 tion of o and r sometimes appears, though the ends are gen- 

 erally etched and corroded. Crystals of all sizes, from that of 

 a needle up, are found penetrating large crystals of quartz and 

 feldspar. 



Figures 9, 10 and 11 are end views of crystals so distorted 

 as to be difficult to put under any special types. In fig. 9 the 

 directions of the prism faces are not preserved on the crystal, 

 so the outline was drawn as nearly as possible like the original. 



