Professor Blum on Pseudomorphic Minerals. 165 



factory manner, that the pseudomorphoses were formerly 

 Nepheline. Spreustein from Wernerite I have never met 

 with." 



The alteration in these two cases commenced at the sur- 

 face of the crystals, spreading from thence to the interior; 

 and this process may he observed in various individuals, 

 which are found in its most various stages. Whilst the 

 above-mentioned small crystal is changed into spreustein 

 merely at its surface, the large one mentioned by Dr Krantz 

 (which is about H in. long by 1 in. in thickness, and is broken 

 off at both ends) consists at one end entirely of an aggregate 

 of red and white spreustein, but at the other still contains a 

 nucleus of nepheline, surrounded by a crust of whitish-red 

 spreustein of from one to two lines in thickness ; and other 

 crystals, again, are entirely changed into the latter substance. 

 Even crystalline particles of Elaeolite have undergone this 

 change. The surrounding felspar (orthoklas) is for most 

 part perfectly fresh, merely exhibiting here and there, at its 

 points of contact with the Spreustein, a slight red colour, 

 arising from oxide of iron, which has interpenetrated its 

 cleavage surfaces. The process of transmutation itself con- 

 sists in a loss of potash, in the emission of a small quantity 

 of natron and alumine, and the absorption of water, whereby 

 (Na, Ka) 2 Si + 2Al Si becomes Na Si + Al Si +2H. And 

 this process occurred in a rock, which — although water was 

 the agent — presents a perfectly fresh character. Nor will 

 it ever occur to any one that the natrolite was here an ori- 

 ginal formation, or that the water was originally present ; 

 for the pseudomorphous nature of the spreustein crystals is 

 too plain to be called in question. They are not genuine 

 crystals ; for they consist of a mass of which the composition 

 is confusedly radiated, (whence the name Spreustein given 

 them by Werner) — of an aggregate, which sometimes even 

 includes a nucleus of the original mineral. But if it must 

 be admitted to be a transformation, then it is a transforma- 

 tion that can have been effected only by means of water 

 which has penetrated into the mineral, extracted and re- 

 moved constituents of the Nepheline, partly deposited itself 

 in their room, and formed mesotype ; for the phenomenon can- 



