large Crystals of Enstatite. 385 



Also it is to be noticed that the crystal was measured at Chris- 

 tiania, and that the faces denoted by Greek letters were deter- 

 mined at Bonn. Having in view the imperfections of the faces, 

 it would not have been possible to obtain measurements more 

 nearly approaching to the calculated angles. 



Fig. 5 represents a crystal of the Museum of Bonn : 5 is a 

 portrait of the crystal ; 5 a and 5 b are more ideal representa- 

 tions. We have the following combination : — 





T=(fa :§&: 

 k = ( oca : 2b : 



c), 

 <0, 



iP'QO, 





q = ( oo a : •§& : 



'.*), 



§P», 





i|r = (ooa: 6b : 

 m — (a : b : ace 



), 



ooP, 





b =(ooa : b : < 



xc), 



goPgo. 



" 



Measured. 





Calculated. 



m 

 k 



f l 



T 

 T 



t m / = 88 

 : b =106 , 

 :b =110 30 

 : k =169 

 :q = 

 :m=120 





o ' / 

 88 16 



105 56 

 110 50£ 

 169 30 

 159 51f 

 118 40 



We remark already a certain asymmetry in this crystal, as 



rements : ■ 



Calculated. 



is to be seen in the following measurements: — 



I 101° V. 



k: m =101 57 

 k: m'= 99 24 f 



The pyramid r, not yet observed in enstatite and hyper- 

 sthene, has been determined by the horizontal edges formed 

 with the prism m as well as through the parallelism of the 

 edges t : q: r / . The dimensions of that crystal are — altitude 

 7 centims., breadth 8 centims., thickness 9 centims. The 

 crystal is broken parallel to two prismatic faces. 



Fig. 6 is very much like the preceding : 



Measured. Calculated. 



m : m / = 88 



O / 



t : m =118 



118 40 



t: a =109f 



110 8i 



t Mean of ten measurements between 99|° and 99^°. 

 Phil Mag. S. 5. Vol. 2. No. 12. JS r ov. 1876. ' 2 C 



