Count de Bournon on Bardigllone. 371 



The only crystals of this substance in which I have found per- 

 fectly determinate forms, except the primitive prisms and its fragments, 

 have occurred to me in the bardiglione from Hall, in specimens that 

 included groups of these crystals. Most of them, though having 

 secondary faces, are so united together, commonly in a direction 

 parallel to their planes, that, till they were broken, and their planes 

 thus exposed, they appeared absolutely to compose but one crystal, 

 as is also the case in the laumonite. Owing to this their addi- 

 tional faces are most frequently destitute of that lustre, which com- 

 monly belongs to the crystals, and are even in general striated. The 

 fractures made in the direction of the diagonals, which are difficult to 

 obtain, are likewise usually striated, thus exposing to view the edges 

 of the lamincE placed on the planes of the prism, especially on those 

 which have a pearly lustre. 



I have represented at fig. 23, that which was already given at fig. 

 14, but of which, in the crystal that has furnished me with the 

 variety I possess, as well as all those I have inserted in the plate 

 annexed to this work, one part alone is in a state of perfect preser- 

 vation. I placed this crystal so, that I could show the natural inte- 

 rior joints, as they are perceived in looking through its terminal 

 faces. The lines that indicate these joints are very conspicuous 

 in it. The two planes 1 and 3 are equally devoid of all lustre and 

 striated, and both of them appear parallel to the interior joints. That 

 marked 1, which I consider as belonging to a fracture, and which 

 might have been produced by a retrogradation by a single row 

 along the edges of the prism with square bases, makes with the 

 faces of the primitive crystal adjacent to it an angle of 135°. That 

 marked 3 appears to answer to r fig. 24. pi. II. of the Abbe Haiiy*s 

 Tableau Comparat'if ; but instead of making with the primitive planes 

 an angle of 129° S^^ as mentioned by that celebrated author, that 



3 A 2 



