Mr Haidinger on the Parasitic Formation of Minerals. 275 



Paramatta, Mar. 26, 1813, 8° 47.5' E. 



27, - 50.5 



31, - 43.5 



Halan, 



Havre de la Co- 

 quille, Duperrey, June 1823, 9 20.5 



Art. XIII. — On the Parasitic Formation of Mineral Species, 

 depending upon Gradual Changes which take place in the 

 Interior of Minerals, while their External Form remains the 

 same. * By William Haidinger, Esq. F. R. S. Edin. 



The mutual attraction of the elements of mineral bodies can- 

 not at present enter into play on so extensive a scale as during 

 the formation of those enormous masses of rocks which form a 

 great portion of our globe ; for these bodies are the result of 

 the very action of the elements on each other, by which they 

 have arrived at a settled state. There are some agents, how- 

 ever, which we daily observe to affect the constitution of mine- 

 rals that are prone to decomposition. Many species of the 

 class of salts are continually destroyed by their solution in wa- 

 ter, and regenerated by its evaporation. Iron-pyrites, ex- 

 posed to the alternating influence of water, the oxygen of the 

 atmosphere, and natural changes of temperature produced 

 in the course of the seasons, or by the decomposition of the 

 substances themselves, will effloresce, and yield sulphate of 

 iron. Heat, and the disengagement of powerful acids from 

 active volcanos and burning coal-seams, give rise to the for- 

 mation of a number of new substances, while those which ex- 

 isted before are destroyed. Usually even the last trace which 

 could lead us to discover from what source the new substances 

 draw their origin is lost ; but there are examples in which the 

 form peculiar to the crystals of the decomposed substances is 

 entirely preserved, while the rest of their properties undergo 

 greater or less changes. The consideration of these constitutes 

 the object of this communication. 



These mineral productions have been called pseudomorpho- 

 ses, a name expressive of their nature, if we attend only to 

 etymology, since the form is not the one belonging to the sub- 



* Abridged from the Edinburgh Transactions, vol. xi. part i. p. 73. 



