MINERAL TRANSFORMATIONS. 



AMONG the most interesting problems which present 

 themselves to the mineralogist are those relating to 

 the "Life-history' of minerals, if such an expression may 

 be used to include their mode of orimn, the chancres to 

 which they are liable and their decay. 



Few minerals are able to resist the transforming in- 

 Muences which operate in the crust of the earth ; the 

 changes of temperature and pressure, contact with air, 

 water and the liquids and gases which they contain, to- 

 gether with the slow but continued action of permeating 

 solutions and of electrolytic processes. Apart from the 

 constituents of certain deep-seated and comparatively un- 

 altered igneous rocks, there are few, if any, minerals which 

 have not resulted from the change, decay, or destruction of 

 pre-existing minerals, and, conversely, few exist which are 

 not destined in due course to beget by their disintegration 

 certain other minerals. The history of their transforma- 

 tions possesses, therefore, a double interest, both as indicat- 

 ing the probable nature and order of the chemical and 

 physical processes to which they have been subjected, and 

 as a clue to the nature and constitution of the minerals 

 themselves. To geologists and mineralogists they are for 

 these reasons equally attractive subjects for study. 



The problems involved are beset with peculiar dif- 

 ficulties ; the initial conditions under which most minerals 

 were formed are hard to realise and impossible to reproduce ; 

 the processes to which they have been subjected have operated 

 for such long periods that experimental evidence can rarely 

 be used for comparison. 



Again, though it may be certain that a given mineral is 

 the result of alteration, the greatest uncertainty often pre- 

 vails as to the nature of the original substance, and, further, 

 in many instances where the nature of the initial mineral 

 is beyond doubt, its decomposition products may appear to 

 be ill-defined mixtures which it is hopeless to identify with 

 any known species. 



