16 



Characters of 

 the new spe- 

 cies diopside. 



Determinate 

 »anetics of 

 form, 

 primiiive. 



pidodecaedral 



ON THE DIOPSIDE. 



this task upon myself, and drew up an article on the subject 

 for the Journal des Mines, persuaded, that these new obser- 

 vations could not fail to be interesting to its readers. This 

 I now purpose to perform, tracing here the principal charac- 

 ters of the two substances discovered by Mr. Bonvoisin. 



Characters of the diopside. 

 Its specific gravity is 3'2374. It does not scratch glass, or 

 very slightly ; but scratches fluate of lime. Before the blowr 

 pipe it fuses into a glass of the same greenish colour as the 

 mass itself. Jta primitive form is a right angled quadrangu- 

 lar prism, PI. I, hg. 5, with oblique bases, the angle of inci- 

 dence between the diagonal drawn from A to O and the edge 

 H is 107° 8'. The prism is subdVisible by very clean sec- 

 tions in the direction of the diagonals of its bases}:. The 

 divisions parallel to the bases are in general very clean; 

 those that answer to the sides m m are less easy to obtain. 



I. Determinate varieties of form. 

 The two principal varieties pointed out by Mr. Haiiy are, 

 lot variety, Primitive diopside: a variety of the mussite 

 of Mr. Bonvbisin. Fig. 5. 



Care must be taken, not to confound the joints exposed 

 on breaking the crystals exhibiting this variety with its na- 

 tural bases. 



2d variety, Didodecaedral diopside, fig. 6. A twelve-sided 

 prism, terminated at each extremity by six faces, situate two 

 and two, one above the other. 



The angle of incidence between M and Mh 90* 



r and M 135° 

 s and M 

 p and r 

 n and r 

 I and s 

 I and p 

 t and s 

 x and r 

 I and M 

 I and rhe sur. 

 face contiguous to S, behind the crystal, 117° 55' 



This 



% If from the point O a perpendicular be let fall on the side opposite 

 to the edge H, the ratio between this perpendicular and the part inter- 

 cepted 



