. 165. OF THE STRUCTURE OF MINERALS. 



minerals cleavage may be effected in still more directions, 

 differing in number, and often in quality. The direc- 

 tion of cleavage more particularly regards such as produce 

 the most apparent faces of cleavage. If two directions 

 of cleavage exist at the same time in a single individual, 

 wherever the faces corresponding to them are obtained, 

 they always intersect each other at the same constant 

 angles. This is a necessary consequence of the parallelism 

 of all those faces of cleavage, which lie in one and the same 

 direction. 



. 165. CHARACTER OF CLEAVAGE. 



The Character- of cleavage consists in the con- 

 stancy of its direction (. 164.), and in the possibility 

 of separating the particles of individuals in this di- 

 rection, as long as the acuteness of our senses, and 

 the delicacy of our instruments will allow. 



There are minerals whose particles may be separated 

 from each other in faces which are regularly situated in 

 respect to the crystalline forms, but which exist previous 

 to the actual division. Those masses, however, which are 

 contained between two such faces, allow of no farther cleav- 

 age. This property of certain minerals will be considered 

 more particularly in . 1 79. It is, however, very distinct 

 from real cleavage, the character of which consists in the 

 possibility of continuing it, as long as our senses may per- 

 ceive it, or our instruments and contrivances may answer 

 the purpose. 



Experience shews that cleavage indeed does possess this 

 property, since it may be effected, to whatever point of the 

 cleavable individual the instrument is applied in the re- 

 quired position. If, therefore, an individual is cleavable 

 in the direction of a certain plane, it must also be cleavable 

 in any other plane parallel to the former, the distance of 

 these planes being less than any given straight line. 



