.181.182. OF COMPOUND MINERALS. 

 . 181. IMITATIVE SHAPES. 



The shape of a compound mineral is called an 

 imitative or particular external Shape, if it bears 

 some resemblance to the shape of another natural 

 or artificial body. Some of these forms are pro- 

 duced in a space not incumbered with matter, and 

 depend upon the properties peculiar to the minerals 

 themselves, without being influenced by any con- 

 tiguous matter ; others owe their shape to that 

 extraneous or foreign matter, with which they are 

 surrounded. The latter of these have been called 

 extraneous imitative Shapes. 



The groupes and geodes are the simplest modes in which 

 the irregularly compound minerals appear in nature. If 

 the individuals thus connected are diminished in size, and 

 if their number at the same time increases, imitative 

 forms are produced from the groupes of crystals ; which, 

 although they are founded in the nature of the individuals 

 themselves, yet. cannot be employed to any useful purpose 

 in Natural History. The extraneous imitative forms can- 

 not be brought into any connection with these groupes 

 at all ; they do not depend upon the natural forms of 

 the individuals ; on the contrary, in most cases where they 

 are observable, we find them quite contradictory to the na- 

 ture of the individuals which they contain. For in these 

 the form depends entirely upon the shape of the space pre- 

 viously existing, and is accordingly entirely accidental. 



. 182. IMITATIVE SHAPES ORIGINATING IN THE 

 GROUPES OF CRYSTALS. 



The imitative shapes which originate from the 

 groupes of crystals, are loose or imbedded, and 

 more or less regular, globular or spheroidal masses. 



