. 192. OF COMPOUND MINERALS. 273 



them, and the splintery fracture therefore does not occur 

 in perfectly opaque minerals. It may occur at the same 

 time with the conchoidal, or another kind of fracture. 

 This has been expressed by the phrases : conchoidal in the 

 grca^ splintery in the small, &c. 



5. The Hackly Fracture, which has been sufficiently ex- 

 plained above (. 172.). 



G. The Slaty Fracture, which resembles imperfect faces 

 of cleavage (. 163.), and partly arises from it. It is met 

 with in the different kinds of Slate, which, for the greater 

 part, are compound minerals, or even mixed, although they 

 appear to be simple. The slaty fracture keeps a constant 

 direction, and is in this respect analogous to cleavage. 



7. The Earthy Fracture, which is the same as the uneven 

 fracture, except that it occurs in decomposed minerals. 



The particles into which compound minerals may be 

 broken, are termed Fragment!!, and their shape is irregular. 

 According to the quality of their edges, they have been di- 

 vided into sharp-edged and Hunt-edged fragments. Slaty frac- 

 ture produces tabular fragments ; thin columnar composi- 

 tion produces splintery fragments. 



. 19&. COMPOSITION IS OF LITTLE VALUE IN NA- 

 TURAL HISTORY. 



It is impossible to derive characteristic terms for 

 the determination of the natural-historical species, 

 from the occurrences of composition. Hence they 

 are of use in the Natural History of the Mineral 

 Kingdom, only in so far as their knowledge is ne- 

 cessary for ascertaining the existence of the simple 

 mineral in the compound. 



Among the various impediments that have retarded the 

 progress of the science, and, in particular, the correct de- 

 termination of the natural-historical species, one of the most 

 conspicuous was the occurrence of individuals in compound 



VOL. i. s 



