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On the Chemical ConMution of' Harinotome, or Cross-stoue. 

 By Arthur Connell, Esq., F.R.S.E. Communicated by 

 the Author *. 



In examining some specimens of harraotome from Strontian, I 

 observed some crystals which appeared to present a very dif- 

 ferent aspect from the ordinary harmotome with which they 

 were associated. The usual crystals of this mineral from the 

 above locality arc well known to be of considerable size, and to 

 exhibit the form of a rectangular prism, Plate I. Fig. 1, termina- 

 ted by a pyramid, the faces of which are set on the lateral edges of 

 the prism, two opposite edges of the pyramid being also replaced 

 by planes. On the other hand, the crystals to which I have re- 

 ferred were a great deal smaller in size, usually not exceeding 

 one-tenth of an inch in length, and of greater transparency ; 

 and they presented the apparently very dissimilar form of a 

 rhombic prism, Fig. 3, of considerable acuteness, having the 

 acute angle more or less truncated by the face A, and termi- 

 nated by a pyramid C, the faces of which were set on the late- 

 ral planes of the prism, and its apex truncated. They were 

 spread over the surface of calcareous spar in considerable num- 

 bers, and were usually attached to the matrix by one of the ex- 

 tremities D'D. Farther consideration, however, showed that 

 this latter form was in reality merely a modification, although 

 undoubtedly a very considerable one, of the old form, and 

 arose principally from the vertical contraction of the crystal, 

 Fig. 1, and its horizontal elongation in the direction of the faces 

 BB', the inclination of the several faces to one another remain- 

 ing always the same ; as will be evident by comparing Figures 

 1 , 2, and 3, Fig. 2 representing another form of the crystal, which 

 may be regarded as intermediate between Figs. 1 and B, and the 

 whole three being placed in parallel position, with tlieir corres- 

 ponding faces marked by the same letters. In some rare in- 

 stances, the pyramids C C, and the face A, Fig. 3, almost en- 

 tirely disappear, so that the crystal appears nearly as a simple 

 rhombic prism ; and in others equally rare, the face D almost 

 disappears, so as to leave the pyramid nearly without truncation. 

 • Read to the Royal Society of Eclinbui-gh, 2d April 1832. 

 VOL. XIII. NO. XXV. JULY 1832. C 



