Professor Blum on Pseudomorphic Minerals. 163 



sist entirely of a fine scaly aggregate of very minute mica- 

 ceous lamellae. Thus Giesecke is neither more nor less than 

 Elaeolite in process of transformation into mica, at one stage 

 of which a condition resembling Pinite, I believe, occurs very 

 frequently. The final result of the transformation is here 

 likewise mica ; and with this view both the chemical compo- 

 sition of the mineral, and the mode in which it is affected by 

 the blowpipe and by acids, closely coincide. Whilst the 

 Elaeolite fuses before the blowpipe, and under the action of 

 acids dissolves and forms gelatine, Gieseckite is but slightly 

 affected by the latter, and is likewise more difficult of fusion. 

 If we compare the results of analysis, — that of the green 

 Elaeolite of Fredericksvarn by Scheerer (a), with that of 

 Gieseckite by Stromeyer (5), — the process of alteration be- 

 comes very apparent. Their constituents are : — 



(a) 







(£) 



Silicic acid, 



45-31 





46-0798 



Alumine, 



32-63 





33-8280 



Natron, 



15-95 





0-0000 



Potash, 



5-45 





6-2007 



Oxide of iron, 



0-45 



Protoxide of iron, 



3-3587 



Chalk, 



0-33 



Magnesia, 



1-2031 



Water, 



0-60 



Oxide of manganese, 



4-8860 





100-76 



1-1556 



96-7119 



According to these analyses, there must have been a loss of 

 natron and an absorption of protoxide of iron and water, to- 

 gether with a small quantity of magnesia and oxide of man- 

 ganese. 



Under the name of Bergmannite or Spreustein, there has 

 long been known a mineral which has been regarded by some 

 mineralogists as a distinct species, and by others as a variety 

 of Wernerite. It is not unfrequently found as a secondary 

 constituent of zircon syenite in Norway, especially in the 

 environs of Brevig, Laurvig, and Fredericksvarn. Scheerer, 

 to whom the external appearance of the Spreustein seemed 

 to indicate that it was not a variety of Wernerite, subjected 

 it to an analysis of which the results are given (Annalen, 



L2 



