128 Messrs. Deville and Caron on Apatite, Wagnerite, 



where it is to be noticed tli.at in either Table eacli non-consecu- 

 tive duad of any pentad occurs once, and only once, as a non- 

 secutive duad of another pentad. The restriction that a non- 

 consecutive duad of any multiplet is not to occur as a duad, 

 consecuti\'e or uon- consecutive, of any other multiplet (see my 

 note appended to Mr. Kirkman's paper " On Autopolar Poly- 

 hedra," Phil. Trans. 1857, p. 183), applies only to ordinary 

 polyhedra, and not to the class here considered. 



2 Stone Buildings, W.C, 

 January 13, 1859. 



XX. On Apatite, Wagnerite, and some artificial species of Me- 

 tallic Phosphates. By Messrs. H. Sainte-Claire Deville 

 and H. Cauon*. 



AMONG the more abundant minerals is found a well-defined 

 and crystallized substance, the phosphate of lime^ which 

 is principally met with in veins in the older rocks and in volcanic 

 lavas. The singular composition of apatite, first determined by 

 M. Gustav Rose in 1827^ shows that it is a definite compound 

 of chloride and fluoride of calcium with phosphate of lime. The 

 chemical examination of this substance, and the establishment 

 of its analogies, formed an interesting subject of inquiry ; and 

 the researches which we have undertaken have led to results of 

 great simplicity. 



By the side of apatite is placed another mineral, Wagnerite, 

 composed of the same or analogous elements, but in different 

 proportions. The calcium of the apatite is replaced by magne- 

 sium ; in addition to which, apatite is a regular hexagonal prism, 

 while Wagnerite is an oblique rhomboidal prism. Their form 

 and composition thus distinguish them from each other, and we 

 shall show that each may be considered as the type of two groups 

 of which we have established all the species. 



Apatite has the composition 



3(P0^3CaO)|p^|Ca; 



Wagnerite is represented by the simpler formula, 



(P0^3MgO)|^^J.Mg. 



AVe have prepared the apatites and Wagnerites which form the 

 species of these two groups, and which are comprised in the fol- 

 lowing list : — 



* From the Comptes Rendus, December 20, 1858. 



