386 



Count de Bournon on Bardiglione, 



TABLE OF THE MODIFICATIONS OF THE PRIMITIVE CRYSTAL 

 OF BARDIGLIONE. 



Primitive Crijstal. A rectangular tetrahedral prism, the terminal faces of which are squares, and 

 the height of which is yet unknown. 



Number 

 of the 

 modifi- 

 cations. 



-s 



Angles of incidence between the 

 new planes, and the sides of the 



Angles of inci- 

 dence of the new 

 planes with each 

 other above those 

 of the prism on 

 which the clea- 

 vage is least easy. 



Nature of the retrogradations. 1 



primitive crystal. 



On the sides of 

 the prism, on 

 which the clea- 

 vage is most easy- 



On the others, 



considered as 



auxiliary. 



On those on 

 which the clea- 

 vage is most easy 



1 On the others. 



Retrogradations along the longitudinal edges of the primitive crystal. 1 



1st. 



.i 

 1 



1 



I 



u 



II 



1° 



'b 



1 

 . . 135» 135° .... 





Retrogradation 

 by a single row . 



Retrogradation 

 by a single row. 



2d. 



. . 108', 27' . . . . 161°, 33'. . 



. . 143°, 6'. .. 



Retrogradation 

 by 1 row in 

 breadth, and 3 

 laminx in height. 



Retrogradation 

 by 3 rows in 



breadth. 



3d. 



. . 116°, 34'. . . . 153°, 26'. . 



. . 126°, 52'. . 



Retrogradation || R.^rogradation 



^^ U '°^A '9 bv 2 'rows in 

 breadth, and 2 - ^ 



lamuise in height. 1 



4th. 



. . 128°, 40'. . . . 141°, 20' . . 



. . 102°, 40' . . 



Retrogradation j Retrogradation 

 by 4 rows in j by 5 rows in 

 breadth, and 5 9 breadth, and 4 

 lamince in height. ! lamim in height. 



5th. 



. . 141°, 20'. . 



. . 128°, 40'. . 



. . 77*, 20' . . 



1 



Retrogradation 

 by 5 rows in 

 breadth, and 4 

 lamioiE in height. 



Retrogradation 

 by 4 rows in 

 breadth, and 5 

 laminse in height. 



Gth. 



. . 161°, 33'. . 



. . 108°, 27' . . 



. . 3G°, 54' . . 



Retrogradation 

 by 3 rows in 

 breadth. 



Retrogradation 

 by 1 row in 

 breadth, and 3 

 lamina; in height. 



Note. As all these modifications, except the first, undergo no retrogradation at the edges of the prism, but on one 

 side, I have noticed this retrogradation only with regard to that side on which the cleavage is expressed, pointing out 

 at the same time the auxiliary retrogradation on the other side. 



This table, together with the plate, displays the singularity I have just mentioned ; which is, that all the crystals of 

 this substance undergo no decrement except on one of the two planes that form each edge of the prism. The fourth 

 and fifth modifications may be considered as forming but one ; and the .same m^y be said of the second and sixth : but 

 to render the details respecting tho crystallization of this substance more methodical, I have considered each of the 

 retrogradations with respect to those sides of the prism on which the cleavage is easiest. In this view, each of these 

 modifications is perfectly distinct from the other ; and while one takes place on llicse laces, the auxiliary retrogradation 

 ii produced.on the adjacent faces, which are those on which the cleavage is least easy. 



