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XX XIV. Oti the CvystallograpJiical Identity of certain 

 Minei-als. By H. J. Brooke, Esq., FJi.S., <St.* 

 [With Figures : Plate I.] 

 L CffZeagonite, Gismofidin, Abrazite, Aricite, and Phillipsite, 



nPHE figures 1 to 4, Plate I., will explain the crystalline 

 -■• relations of these differently named minerals. Fig. 1. 

 is the form of Phillipsite, the crystals being composed of 

 two or four simple crystals arranged in a manner analogous 

 to those of Harmatome ; I am not, however, aware that any 

 crystals have yet been found which exhibit this structure as 

 distinctly as in Harmatome. 



The line a b, fig. 1, is in most crystals slightly raised above 

 the surface, marking the lines of junction of the twin crystals ; 

 but in some crystals it is scarcely perceptible, and I have 

 found the inclination of d d', fig. 2, on crystals with bright 

 faces, differing so little from 90° as to induce my assuming that 

 as the true angle. On one specimen in my possession there 

 are both opake and transparent crystals resembling fig. 1, 

 proving that opacity is not a distinguishing character of this 

 variety of Zeagonite. 



Fig. 2 exhibits the first step in the passage of fig. 1 into 

 figs. 3 and 4. I have several instances of two crystals, or 

 bunches of crystals, crossing atright angles and producing the 

 rudiment of the octahedron, fig. 3, the faces of this octa- 

 hedron being so marked in all the crystals I have seen as to 

 indicate its compound structure. I have observed three mi- 

 nute crystals crossed as in fig. 2, on a specimen in the British 

 Museum explanatory of the crossed octahedron, fig. 4, for a 

 very distinct specimen of which I am indebted to the liberality 

 of Mr. Heuland. 



It thus appears that there is no other difference between the 

 crystals of Phillipsite and the other varieties of Zeagonite than 

 in the greater or less complexity of crystalline composition. 



II. Of Mtirckisonite, Moonstone, and the iridescent Felspar 

 from Fredricksvarn, Norway, 



These have the same cleavages, the same angular measure- 

 ments; and the play of light is observable in the same di- 

 reotion on the pa»'ticular cleavage plane, by which Mr. Levy 

 distinguished the Devonshire Murchisonite from common fel- 

 spar. 



The three varieties may therefore now be classed together 

 as Murchisonite f. 



* Communicated by the Author. 



t Mr. Levy's original paper upon Murchisonite will he; found in Phil. 

 Mag. and Annals, N.S. vol. i. p. 448. —Edit. 



