Observations on Pseudomorphism. 81 



Art. VIII. — Observations on Pseudomorphism ; by J. D. Dana. 



Notwithstanding the exact balancing of chemical formulas 

 which we find through Dr. Blum's work, there is yet much 

 mystery with regard to the origin and formation of Mineral 

 Pseudomorphs. The elements removed and the amount added, 

 may be laid down with mathematical exactness, but that the 

 change has consisted in precisely such a removal and addition, is 

 by no means sure. Moreover, in searching for the causes of 

 pseudomorphons changes, it appears to have been too much the 

 method to look for distinct causes for each separate instatice of 

 pseudomorphism: whereas we deem it probable that some few 

 general principles will yet be ascertained, that will embrace and 

 explain the whole subject. 



Although we cannot hope to remove all the obscurity that 

 rests about this subject, yet we may venture to offer some con- 

 siderations in its elucidation, such as appear to result from the 

 known causes acting in nature, and the facts that have passed in 

 review. Could we believe with some late chemists, in the trans- 

 mutation of the elements, we should consider this a fruitless sub- 

 ject of investigation, since in the midst of the many possibilities 

 which such an hypothesis creates, we should hardly know which 

 to choose. But the received principles of chemical science, are 

 believed sufficient for these explanations, without the aid of such 

 speculations. 



Viewing pseudomorphs with reference to their origin, we may 

 make the following distribution of them: those produced, 



1. By Infiltration ; in which a cavity previously occupied 

 by a crystal, is refilled by some other mineral. A cubic crystal 

 of salt in clay, is removed by percolating water, and the cavity 

 afterwards filled with gypsum. In this there is nothing chemi- 

 cal ; it is simply a mechanical deposition into a ready formed 

 mould. 



2. By Incrustation ; in which a mineral incrustation covers a 

 crystal, which crystal is subsequently removed by some process 

 of solution. Like pseudomorphs by infiltration, this process is 

 mechanical — a simple deposition of foreign matter aronnd a crys- 

 tal. The process by which the original crystal was removed is a 

 separate enquiry, and one of much interest. 



Vol. xLviii, JMo. 1.— Oct.-Dec. 1844. 11 



