644 Cook and Kraus — Datolite from Great Notch. 



are free from coatings. On account of the waviness of the 

 faces of e ^ 112 J, the pyramid n {111} exhibits a comparative 

 brilliance which makes it, next to the peculiar type of develop- 

 ment, the most striking feature of the crystals. The other 

 pyramids, with the exception of X { 113 } , oc { 124 } , and Y 1 { 134 \ , 

 appear as bevelings between the more prominent faces. 

 A { 1135 when present show small triangular faces, and oc 5 124 \ 

 and YJ134} form w T ith the clinodome g {012} a rounded sur- 

 face. Of the clinodomes, only m^jOll} is always present. It 

 hascom paratively large faces and is always coated. #{012}, 

 when it occurs, appears as small triangular faces. The pina- 



Fig. 2. 



x^a. 



coid a {100 } is always present with small triangular faces, 

 while b {010} appears occasionally beveling the edge between 

 the faces of the clinodome ^{Oll}. 



The goniometric measurements upon which the orientation 

 of the crystals is based are as follows : 











Obser 



ved. 



Calculated.* 



m 



: m" 



= (no) 



: (iio) = 



64° 



46' 



.64° 



49' 



m x 



: m' x 



= (on) 



: (oil) = 



103 



26 



103 



22 30 



in 



I X 



= (no) 



: (102) = 



52 



56 



53 



15 



111 



' y 



= (iio) 



: (111) = 



22 



44 



22 



57 



a 



: x 



= (100) 



: (102) = 



44 



56 



45 



00 



9 



: (/ 



= (012) : 



(012) = 



64 



42 



64 



38 30 



n 



: n!" 



= (in) 



: (Hi) = 



59 



39 



59 



4 30 



a' 1 



1 e 



= (loo) 



: (112) = 



49 



48 



49 



57 



e 



. r 



= (112) 



(112) = 



48 



46 



48 



19 



A 



: A' 



= (113) : 



(113) = 



39 



10 



38 



45 30 



a 



:j 



= (100) : 



(502) = 



10 



42 



11 



20 



* These are the values variously calculated by Dana, Ungemach, and Kraus 

 and Cook. 



