Prof. Maskelyne and Dr. Lang's Mineralogical Notes. 45 





a(100). 



5(010). 



e(001) lw(110). 



£(101). 



m(011). 



z(lll). 

 33 34 



w(110) 



45 30 



/ 



44 30 



90 6 



O 1 







59 24 



58 3i 



n (2 1 0) 



26 58 



63 2 



90 



18 32 



49 40 



70 37 



37 49 



h (101) 



43 26 



90 



46 34 



59 24 







62 5 



36 28 



M(011) 



90 



42 56 



47 4 



58 31 



62 5 







35 44 



ah 11) 



54 16 



53 32 



56 26 



33 34 



36 28 



35 44 







o (1 1 3) 



71 40 



71 20 



26 40 



63 20 



32 33 



32 32 



29 46 



/(311) 



24 52 



72 5 



73 21 



31 10 



23 47 



65 8 



29 24 



2/(313) 



48 7 



76 10 



45 11 



50 41 



13 50 



48 36 



22 38 



The crystals are all very small (about one-tenth of an inch 



across) and colourless; they occur in the cavities of a white 



mass, probably of the same chemical composition. The crystals 



being elongated parallel to the axis c, are combinations of the faces 



abmnz o, PI. Ill, fig. 1. I found on a crystal of this kind the 



angles ° Q • 



mz = 33 30, 



mo = 63 30. 

 The face / was observed cutting off the edge formed by the two 

 faces (1 1 1) and (1 1 0), and lying in one zone with them. I 

 measured 



(111)/ =59 17(59 40calc.) 



(111)(110) = 91 14(90 50 „ ) 



Considering that the face was not very perfect, I think these 

 angles afford a sufficient ground for assuming the symbol of / to 

 be (3 11). 



Another crystal on which the faces of the prism m were tole- 

 rably good yielded me the following values for the angles of the 

 prism : — 



(110)(110) =90 37 

 (ll0)(IT0) = 89 26 

 (ll0)(l] .0) =91 1 

 (110)(110) = 88 56 



Hence we see that, although the faces (1 10) and (110) are 

 pretty nearly parallel, as we find a mean value of 



(110)(ll0) = 180°0', 



the faces (1 T 0) and (1 1 0) deviate sufficiently from parallelism 

 to give 



(110)(1 10) = 180° 30'. 

 This is another example, in addition to those found by Kock- 



