151 



generally strongly striated parallel to the axis of the zone; it is 

 therefore only in rare cases that accurate values of the angles 

 in this zone can be obtained. The crystals are generally ter- 

 minated by d and c. The faces belonging to the form d are, 

 as a rule predominant. Sometimes с is totally absent (Fig. 1). 

 The new form g has been found only on a few comparatively 

 large crystals (Fig. 4). Its faces are large and, like the other 

 terminal faces of these crystals , eminently smooth and 

 brilliant. 



Below' are given the most important of the angular values 

 found by measurement of the elpidite crystals together with the 

 corresponding calculated values. 



Observed 

 а:Ъ = (100) : (OlO) = 89° 56' 

 m:m = (llO) : (iTo) =*o4° 3M 

 m\b = (110) : (010) = 62° 39' 

 m:a = (UO) : (lOO) = 26° 58'. 

 n:n = (120) : (120) = 88° 45' 

 n:m = (120) : (llO) = 18° 28' 

 d:d = (Oil) : (oil) =*88°45' 

 d:c = (on) : (001) = 44° 20' 

 g:c ^ (102) : (OOl) = 43° 48' 

 g:a= (102) : (100) = 46° 8' 

 d:n = (Oil) : (120) = 59° 49' 

 g:d = (102) : (Oil) = 59° 3' 

 g:ti = (102) : (l20) = 60° 40' 



Calculated 



90° 





62° 



58' 



27° 



2' 



88° 



52'" 



18° 



32' 



44° 



22' 



43° 



48' 



46° 



12' 



60° 



1' 



58° 



57' 



6Г 



With regard to diaphaneity elpidite is, as has already 

 been stated, of three kinds: opaque columns, enamel -white 

 crystals, and clear and transparent crystals. The last or the 

 well -developed crystals occur so sparingly and are so small 

 that one cannot from them obtain material for an optical 



