272 TERMINOLOGY. g. 191. 



. 191. STRUCTURE OF COMPOUND MINERALS. 



Thtit kind of structure which has been consider- 

 ed above in the simple minerals, does not occur in 

 the compound ones. If we break them, however, 

 we produce what has been called their Fracture ; 

 and the particles of the mineral separate in the 

 Faces of Fracture. 



If the particles are still distinguishable as individuals, 

 they must be considered according to their respective regu- 

 lar or irregular structure, to their faces of composition, and 

 to every other character which they present to the observer ; 

 in short, they must be considered as simple minerals. In 

 the present place, therefore, only those compound minerals 

 shall be treated of, in which, on account of their minute- 

 ness, the individuals are no longer distinguishable. In 

 these the following kinds of fracture have been distin- 

 guished. 



1, The Conchoidal Fracture, together with its various 

 modifications, which depend upon size, perfection, rela- 

 tive depression (. 172.)- 



2, The Uneven Fracture, which has been subdivided ac- 

 cording to the size of the asperities, into coarse-grained, 

 small-grained, and fine-grained uneven fracture. 



3, The Even Fracture, which arises if the elevations and 

 depressions upon the face of separation nearly approach to 

 evenness. These even parts of the fracture must not be 

 confounded with faces of cleavage, because they do not 

 keep a constant direction, and are only observable in com- 

 pound minerals. This variety of fracture is so very rare, 

 that it is difficult to quote good examples of it. Sometimes 

 it occurs in compact Lead-glance. 



4, The Splintery Fracture, which is produced if upon the 

 face of separation, detached scaly particles remain, joined to 

 the mass by their thicker end. These particles are render- 

 ed visible by that portion of light which passes through 



