260 TERMINOLOGY. . 18G. 



But if an implanted crystal (. 160.) is covered over by 

 the mass of another mineral, which has been formed after 

 the production of the first, the deposite of new individuals 

 will at first constitute a Coating, which consists of minute 

 crystals, and through which the form of the implanted crys- 

 tal still continues to be perceptible ; the mineral may yet 

 proceed in its formation, and become massive, or it may as- 

 sume any other imitative shape, in which the form of the 

 original implanted crystal entirely disappears. The crys- 

 tal is moulded in this mass ; and, if it be taken away, or 

 decomposed, it will leave an Impression of its form. Rhom- 

 bohedral Quartz, and many other minerals, present in- 

 stances of similar impressions. From the form of the im- 

 pression, we may very often infer by what mineral they 

 have been occasioned. What has been called the ramose 

 shape of the octahedral Iron from Siberia, is nothing else 

 but the result of impressions produced by crystals and 

 grains of prismatic Chrysolite. 



The crystals sometimes are again decomposed in the 

 place of their formation, and thus leave the impressions of 

 their form on other minerals, which have escaped this de- 

 struction. If in these empty spaces a new compound mine- 

 ral is formed, it must necessarily assume the shape of the 

 space already existing, since the sides of this become the 

 support of the individuals newly formed. Thus pseudomor- 

 phoses are formed, which appear in the shape of implanted 

 crystals, if the mass containing the impressions, by what- 

 ever circumstances, happens to disappear. 



All the peculiarities of the pseudomorphoses can easily 

 be explained from the mode of their formation now de- 

 scribed. 



The form of the pseudomorphoses has no relation at all 

 to the nature of the mineral in which it occurs. For it 

 is entirely accidental, from what mineral the impression is 

 derived in which the new individuals have been deposited. 

 Hence it is not derived from the composition of the indi- 

 viduals contained in the pseudomorphosis (. 17&). Thus 

 in rhombohedral Quartz we meet with forms originating 



