14 
THE GEOLOGIST, 
RESEARCHES ON PSEUDOMORPHS. 
By M. Delesse. 
Translated from the "Annales des Mines"* by H. C. Salmon, F.G.S. 
(Continued from jjage 453, vol. iii.) 
PSEUDOMOEPHISM. 
When a mineral presents itself under a form whicli does not belong 
to it, there is then what I shall call 'pseudomorphism. 
The substance from which the mineral borrows its form may be of 
any kind — inorganic or even organic. It is called original or pseu- 
domorphosed, while the mineral which replaces it is called pjseudo- 
morphic. 
Pseudomoi^hism by alteration is that in which the pseudomorphic 
mineral still contains the elements of the original substance. l\seu- 
domorphism by disploxement 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- 
pyi'ites, which changes into limonite, still preserving its crystalline 
form ; or fluor, which after being completely destroyed, is replaced 
by quartz. The name of paramorphism has been given to the kind 
of pseudomorphism which is produced wdthout modification of 
chemical composition. Arragonite changed into calcite, and pyi'ite 
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- 
moi'phosed, there is produced what M. Naumann has called zoo- 
morphs and phytomorphs.f 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 
takes place by the same processes. The comparison of the original 
* Vol. xvi., p. 404, 6th livraison: 1859. 
t C. F. Naumann : '* Elemente der Mineralogie," 
