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II. On the Crystallographical Identity of Phacolite and 

 the Irish bipyramidal Levyne with Chabasie. By 



H. J. Brooke, Esq., F.R.S., fyc* 



[With Figures : Plate I.J 



SOME specimens of a mineral in small and nearly transpa- 

 rent bipyramidal crystals have been received in this 

 country from Bohemia ticketed " Phacolite," and other speci- 

 mens in larger crystals of nearly the same form have been sent 

 from Ireland under the name of " Levyne." It does not appear 

 by whom these specimens have been so named, but I find on 

 examination of them that the crystals are alike, and that they 

 correspond in primary form and angular measurement with 

 Chabasie ; the common twin crystals however of this substance 

 consist of only two simple crystals intersecting each other, while 

 those of Phacolite may be most easily explained by supposing 

 them to consist of four. 



As a more perfect knowledge of these composite forms will 

 be useful to mineralogy, I am induced to request a place for 

 the accompanying figures and remarks in the Philosophical 

 Magazine. 



Fig. 1. is a simple crystal of Chabasie, from the combina- 

 tion of two of which, the fundamental crystal, as it may be 

 termed, of Phacolite, No. 2, is produced. The planes o 

 have not been before observed on Chabasie. They result from 



the law B of Hairy, the planes n corresponding to 6, r to fe, 



and u to t). 



Fig. 2. shows the combination of two of these crystals, the 

 planes o coinciding in surface so as to form one plane in the 

 twin crystal, and filling up the re-entering angle in the com- 

 mon twin crystals of Chabasie. 



Fig. 3. Two intersecting crystals which are supposed to 

 cross each other, in the manner represented in the figure, 

 within the crystals represented by fig. 4. 



Fig. 4. The figure of Phacolite, the letters on the several 

 planes indicating its relation to the preceding figures; with 

 this difference however, that the planes corresponding to the 

 P planes of fig. 4 on the actual crystals of Phacolite, are not 

 single as drawn in the figure, but consist of a number of mi- 

 nute similar planes, which recede, as it were, behind each 

 other so as to produce the appearance of rough single planes, 

 nearly parallel to the planes n on which they rest. 



Assuming P on P, fig. 1, to be 94° 46', and denoting the 



* Communicated by the Author. 



