14 



THE GEOLOGIST. 



RESEARCHES 0 N PSEUDOMORPHS. 

 Bt M. Delesse. 



Translated from the " Annales des Mines"* by H. C. Salmon, F.G.S. 

 (Continued from page 453, vol. iii.) 



Pseudomorphism. 



When a mineral presents itself nnder a form which does not belong 

 to it, there is then what I shall call pseudomorphism. 



The snbstance from which the mineral borrows its form may be of 

 any kind — inorganic or even organic. It is called original or pseu- 

 domorpliosed, while the mineral which replaces it is called ptseudo- 

 morphic. 



Pseudomorphism by alteration is that in which the pseudomorphic 

 mineral still contains the elements of the original substance. Pseu- 

 domorphism by displacement is that in which this is not the case. 

 In order to understand the difference which exists between these two 

 kinds of pseudomorphisms, it suffices to mention as examples iron- 

 pyrites, which changes into Hmonite, still preserving its crystalline 

 form ; or nuor, which after being completely destroyed, is replaced 

 by quartz. The name of paramorphism has been given to the kind 

 of pseudomorphism which is produced without modification of 

 chemical composition. Arragonite changed into calcite, and pyrite 

 changed into marcasite are examples. 



At first sight it seems that these metamorphoses of minerals must 

 be very exceptional, but observation teaches us, on the contrary, 

 that they are met with in a number of localities ; they are, moreover, 

 extremely varied. In fact, they include all the alterations to which 

 minerals are subject in their structure and in their chemical compo- 

 sition. They include also, as a particular case, the decomposition of 

 minerals; and kaolin, for example, results from a true pseudomor- 

 phism of felspar. 



When organic bodies, whether animal or vegetable, are pseudo- 

 morphosed, there is produced what M. ISTaumann has called zoo- 

 morphs and phytomorphs.t The pseudomorphism of organic bodies 

 may likewise be established as easily as that of the best crystallized 

 mineral ; for, although the form of these bodies may not be simple 

 and geometrical, it is, however, quite characteristic, and moreover it 

 corresponds to a known composition. Besides, the study of this 

 pseudomorphism is not less interesting than that of minerals, and it 

 lakes place by Hie same processes. The comparison of the original 



* Vol. xvi., p. .101, 6th livraison : 1859. 



+ C. V. Namnann : " Elemente der Mineralogie." 



