TERMINOLOGY. . 171. 



Cleavage is termed Prismatoldal, if it takes place in a 

 single direction parallel to the axis, whatever may be the 

 simple form corresponding to this direction. 



It is said in general to be Monotonous*, if it consists of 

 a single face, which may be perpendicular, or inclined, or 

 parallel to the axis. 



The term Paratomons-\- refers to faces of cleavage of an 

 indeterminate number, parallel to the faces of a finite 

 form, and which therefore are not vertical, nor perpendicular 

 to the axis of the fundamental form. . This expression may 

 also be employed if the directions of cleavage correspond 

 only to half the number of faces of a simple form. 



Cleavage is termed Peritomous $, if it takes place in more 

 than one direction parallel to the axis, and if the faces are 

 all of the same quality and perfection. The result of this 

 cleavage is a vertical prism. 



If the directions of cleavage are parallel to the faces of a 

 vertical oblique-angular four-sided prism, and at the same 

 time to those of a horizontal one, the cleavage is said to be 

 Di-prismatl-c. This di-prismatic cleavage and the prismatoi- 

 dal cleavage is confined to prismatic, hemi-prismatic, and 

 tetarto-prismatic forms. The rest may occur in any of the 

 systems of variable dimensions, which, if necessary, is ex- 

 pressed by Cleavage, rhombohcdral and paratomous, &c. In 

 the peritomous cleavage, the form obtained may be a com- 

 bination ; it is a combination in- the di-prismatic cleavage. 



The expressions employed for the designation of the par- 

 ticulars of cleavage in the tessular system, are evident from 

 themselves, and therefore need no farther explanation. 



. 171. FRACTURE. 



To break a mineral, in order to obtain its Frac- 



* From ftova;, single, and ripvu, I cleave. 

 f From vrxou, about, and ri t uvu, I cleave. 

 From <r*^ x , round, and TJ^W, I cleave. 



