. 187- OF COMPOUND MINERALS. 263 



decomposed individuals. The same takes place if the indi- 

 viduals of compound minerals do not cohere from all sides, 

 so that they allow of the interposition of foreign matter. 

 Thus the cellular shapes arise, of which again the former 

 have been called regular, and the latter irregular cellular 

 shapes. The sides of the alveolae again are sometimes 

 lined with minute .crystals of a third mineral, and this 

 among others is the case in what has been called the cellu- 

 lar P}'rites. In that mineral the sides of the alveolae are 

 perpendicular to each other, because they express the struc- 

 ture of hexahedral Lead-glance ; they consist of rhombohe- 

 dral Quartz, and are lined with crystals sometimes of 

 hexahedral, sometimes of prismatic Iron-pyrites. On this 

 account it is necessary to refer some varieties of cellular 

 pyrites to the one, some to the other species of the genus 

 Iron-pyrites. 



The crystals of Steatite are considered as real crystals by 

 some mineralogists, by others as pseudomorphoses : nothing 

 decisive, however, has been brought forward in respect to 

 this point ; and they require therefore a very accurate exa- 

 mination, to prevent us from forming an erroneous opinion 

 of their nature. 



. 187- IRRKGULAll ACCIDENTAL IMITATIVE 

 SHAPES. 



According to the quality of the space, in which 

 these imitative shapes have been formed, they may 

 be distinguished into : 1, such whose form is entire- 

 ly accidental ; 2, such whose form depends upon 

 particular openings in other minerals, which are not 

 simple ones ; and 3, such whose form depends upon 

 bodies, not belonging to the mineral kingdom. 



In the mass of rocks, and in that of beds and veins, we 

 very often meet with cracks or fissures, which seem to 

 have once been open, or which still continue so. Com- 



