SECTION X. 



EPIGENE AND PSEUDOMORPHOUS 

 CRYSTALS. 



IN addition to the variety of crystals already des- 

 cribed, there are others whose forms are not natural 

 to the substances in which they occur. 



To one class of these the Abbe Haiiy has applied 

 the name of Epigene, where a chemical alteration has 

 taken place in the substance of the crystal subsequently 

 to its formation. 



Thus crystals of blue carbonate, and of red oxide 

 of copper, are frequently found converted into green 

 carbonate. Sulphuret, and carbonate, of iron, are 

 changed into oxides, without losing their peculiar 

 crystalline forms; and the same alteration takes place 

 in other substances. 



Another class of crystals, not belonging to the 

 substances in which they occur, have been denomi- 

 nated Pseudomorphous. These have been formed 

 either within cavities from which crystals of some other 

 substance have been previously removed by some natu- 

 ral cause., probably by solution, or upon crystals of 

 some other substance which have subsequently dis- 

 appeared; the space they occupied either remaining 



