. 186. OF COMPOUND MINERALS. 259 



dividuals, from which we may judge, without giving any 

 attention to the surrounding mass, whether the imitative 

 shape be the result of crystallisation, or whether it has been 

 influenced by other circumstances. 



The space in which the accidental imitative shapes are 

 formed, may be either regular or irregular. A regular 

 space cannot be produced except by crystallisation ; and 

 this may be either in the interior of a real crystal, or it is 

 the cast of a crystal in the surrounding mass (. 186.). The 

 first is not uncommon, particularly in large crystals of 

 rhombohedral Quartz, where part of the space of the crys- 

 tals has remained empty, and is regularly limited by the 

 surrounding crystalline mass. 



The irregular spaces sometimes consist of accidental fis- 

 sures, cracks, and other similar openings : sometimes they 

 depend upon the? structure of the surrounding mass, which 

 in many instances belongs to the class of rocks ; others at 

 last -arise from moulds of various minerals, and also of 

 organic bodies. 



The different description of the space in which compound 

 minerals are formed, produces a distinction of their forms 

 into regular and irregular accidental imitative forms. 



. 186. REGULAR ACCIDENTAL IMITATIVE SHAPES. 

 PSEUDOMORPHOSES. 



The regular imitative shapes of the preceding 

 paragraph have been called Pseudomorphoses, or 

 Supposititious Crystals. The latter denomination 

 seems to be rather improper, since they share so 

 very little in the properties of real crystals. 



No pseudomorphoses are formed in such impressions as 

 originate from imbedded crystals, which can be separated 

 from their surrounding mass (. 160.) ; at least experience 

 has not as yet furnished us with any well authenticated in- 

 stances which could not be explained, but on that suppo- 

 sition. 



