TERMINOLOGY. . 161. 



parated, but not the particles themselves, exists in the mi- 

 nerals, previous to its having been rendered visible by 

 mechanical force. The particles of a mineral therefore 

 necessarily must stand in some regular mechanical con- 

 nexion, because the faces in which they separate are parallel 

 to faces of regular forms. It is by means of the division 

 that we acquire a knowledge of this connexion, or of what 

 is understood by the regular structure of individuals. 



If we divide the particles of an individual in other direc- 

 tions than in those of regular structure, the division takes 

 place not in even faces, but in uneven faces of different 

 descriptions, and by this the regular structure is not ren- 

 dered observable, although it does, or at least may take 

 place in the same individual. These particles no longer 

 possess the property of being regularly divisible parallel to 

 faces obtained by this kind of division ; and the quality of 

 the faces therefore demonstrates, that no regular mechani- 

 cal connexion of the particles can take place in these di- 

 rections. The connexion between the particles in these 

 directions, is also termed the irregular structure. 



It is sometimes attended with considerable difficulty to as- 

 certain the regular structure, and very often it is no less dif- 

 ficult to observe the irregular structure. The particles of 

 certain minerals, as of hexahedral Lead-glance, of rhombohe- 

 dral Lime-haloide, &c., so very readily separate in the direc- 

 tion of their regular structure, that it becomes almost impos- 

 sible to produce any divisions in another direction ; al- 

 though they may allow of such a division. On the con- 

 trary, others separate with much greater facility in every 

 direction but that of the regular structure, so that it 

 likewise becomes difficult to observe even traces of it, 

 though by analogy we are led to suppose the existence of 

 the regular structure. 



The regular structure of minerals is observed in their 

 Cleavage, the irregular structure appears in their Fracture ; 

 both, fracture and cleavage are comprehended under the 

 more general idea of Structure. 



