152 



CONCH o i DAL. 



In the conchoidal fracture, one of the sepa- 

 rated surfaces is concave and the other convex. 

 It is also not unusual for them to be marked by 

 curved undulations more or less parallel, or, at 

 least, respecting, with greater or less accuracy, 

 one centre. 



The conchoidal fracture varies in the degree 

 of curvature, or in the depth of the concavity. It 

 also varies in extent, or in lateral dimensions, 

 Under these several variations, it presents a great 

 diversity of aspect. 



Occasionally, two distinct concavities occur ; 

 the one of a smaller size and within the other. 



A succession of minute conchoidal fractures 

 produces an undulating surface ; sometimes fur- 

 ther becoming splintery. 



The three preceding fractures may be united, 

 or they may pass into each other in various ways. 

 They may also be united with one, or with more 

 than one, of the smaller varieties that follow. 

 The peculiar aspects sometimes found on the 

 surfaces of these larger fractures, are mentioned 

 Hinder the subsequent heads. 



