130 



Mr. Levi/ on a new Mineral. 



[Feb. 



Article VIII. 



Fig. 2. 



Account of a new Mineral. By Mr. A. Levy, MA. of the Uni- 

 versity of Paris. 



(To the Editor of the Annals of Philosophy.) 



SIR, Great Russcll-strcct, Bloonubuni, Jan. 23, 1823. 



In the select collection of minerals lately Mr. Heuland's 

 small private collection, but now the property of C. H. Turner, 

 Esq. 1 found two specimens from the Seisser Alpe in the Tyrol, 

 containing small brilliant transparent crystals, which were 

 described as datolite ; but which, from their crystallographical 

 characters, ought, I believe, to be separated from that mineral 

 species. 



In order that the difference between the two substances may 

 be the better shown, I shall first 

 describe one of the new varieties 

 of datolite which I have observed 

 in the same collection. This va- 

 riety is represented by rig. 2, and 

 indicates for the primitive form a 

 right rhombic prism, the lateral 

 planes of which would correspond 

 to the faces marked in, and the 



base to the face p. Moreover, in 



i 



order to make the face a, the result of a simple decrement on 

 the lateral angles of this prism, it is necessary to determine 

 its height by assuming that the face o 1 is produced by a decre- 

 ment by one row on the obtuse angle of the base. If the 

 height were to be determined by any other condition, it would 



make the faces a the result of an intermediary decrement. The 

 dimensions of the right rhombic prism being thus determined, 

 not only the modifications of the crystal represented in fig. 2, 

 but all that I have observed, result from very simple decrements 

 on its different parts ; there can be no objection, therefore, to 

 consider it as the primitive form. Now I find, by the reflective 

 goniometer, that the incidence of 



P on mis 90° 0' 



monm 103 25 



on p. 



147 46 



The first of these incidences was to be expected from the 

 law of symmetry: it results from the other two, that the primi- 



