COMPOUND MINERALS. 95 



The denomination of crystals to these shapes was, no doubt, first 

 applied from their external regularity ; the slightest attention to 

 their internal structure is sufficient to show the impropriety of such 

 a name, since, in this respect, they share so little in the properties of 

 real crystals. 



No pseudomorphoses are formed in such impressions as originate 

 from imbedded crystals, and which are disunited on all sides from 

 the surrounding mass. But if an implanted crystal (. 54,) is cov- 

 ered over by the mass of another mineral, which has been formed 

 after the production of the first, the deposits of new individu- 

 als will at first constitute a coating, consisting of minute crys- 

 tals, and through which the form of the implanted crystal still 

 continues to be perceptible ; the mineral may yet proceed in its 

 formation, and become massive, or it may assume any other imi- 

 tative shape, in which, the form of the original implanted crystal en- 

 tirely disappears. The crystal is moulded in this mass ; and, if it 

 be taken away, or decomposed, it will leave an impression of its 

 form. Quartz often presents instances of these impressions. From 

 the form of the impression we may very often infer by what min- 

 eral it has been occasioned. Thus, what has been called the ramose 

 shape of the Meteoric Iron of Siberia, is the result of impressions 

 produced by crystals and grains of Chrysolite. 



The crystals sometimes are decomposed in the place of their 

 formation, and compound minerals come in to fill the cavities thus 

 produced ; in these cases, the compound mineral assumes the shape of 

 the space already existing, since the sides of this become the support 

 of the newly formed individuals. After this manner, pseudomorpho- 

 ses are formed, which appear in the shape of implanted crystals, if the 

 mass containing the impressions, by any cause, shall happen to dis- 

 appear. 



All the peculiarities of the pseudomorphoses admit of an easy ex- 

 planation from the mode of their formation above described. 



The form of the pseudomorphoses, has no relation at all to the na- 

 ture of the mineral in which it occurs. For it is entirely acciden- 

 tal, from what mineral the impression is derived, in which the new 

 individuals have been deposited. Thus in Quartz we meet with 

 forms originating from Carbonate of lime, Fluor and from Gypsum; 

 which is sufficient to prove, that the forms of the pseudomorphoses 

 cannot by any means be members in the series of crystallization of 

 those species to which they belong. 



The quality of the surface of the pseudomorphoses, depends only 

 upon its form, and not upon its substance, or its mode of composition, 



