TABLE OF THE MODIFICATIONS OF THE PRIMITIVE CRYSTAL OF BARDIGLIONE.
Primitive Crystal. A rectangular tetrahedral prism, the terminal faces of which are squares, and the height of which is yet unknown..| Number of the modifi- cations |
Figure of the Crystal | Angle of Incidence between the two planes, and the sides of the primitive crystal. | Angle of incidence of the new plane with each other above those of the prism on which the cleavage is least easy | Nature of the retrogradations | ||
| On those on which the cleavage is most easy | On the others | On the sides of the prism, on which the cleavage is most easy | On the others, considered as auxiliary. | |||
| Retrogradations along the longitudinal edges of the primitive crystal. | ||||||
| 1st | Primitive crystal with plane of substitution on its edge. | 135° | 135° | 90° | Retrogradation by a single row. | Retrogradation by a single row. |
| 2d | 106°,27′ | 161°,33′ | 143°,6′ | Retrogradation by 1 row in breadth, and 3 laminæ in height | Retrogradation by 3 rows in breadth | |
| 3d | 116°,34′ | 153°,26′ | 126°,52′ | Retrogradation by 1 row in breadth, and 2 laminæ in height | Retrogradation by 2 rows in breadth | |
| 4th | 128°,40′ | 141°,20′ | 102°,40′ | Retrogradation by 4 rows in breadth, and 5 laminæ in height | Retrogradation by 5 rows in breadth, and 4 laminæ in height | |
| 5th | 141°,20′ | 128°,40′ | 77°,20′ | Retrogradation by 5 rows in breadth, and 4 laminæ in height | Retrogradation by 4 rows in breadth, and 5 laminæ in height | |
| 6th | 161°,33′ | 108°,27′ | 36°,54′ | Retrogradation by 1 row in breadth | Retrogradation by 4 rows in breadth, and 3 laminæ in height | |
Note. As all there 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 may be said of the second and sixth but to render the details respecting the 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 these faces, the auxiliary retrogradation is produced on the adjacent faces, which are those on which the cleavage is least easy.
