Dr. Blum on Pseudomorphoiis Minerals. 69 



Pseudomorph. Form imitated. 



Electric Calamine, Fluor spar, Calc spar, Dolomite, Galena, Pyro- 



morphite. 

 Tin ore. Feldspar. 



White Lead ore, Heavy spar, Fluor spar. 



Peroxyd of Iron, Fluor spar, Calc spar. 



Brown Iron ore, Heavy spar, Fluor spar, Calc spar, Dolomite, 



Quartz, Comptonite, Blende, Galena, Pyro- 



morphite. White Lead ore. Red Copper ore. 

 Pyrites, Heavy spar, Calc spar, Quartz, Brittle Silver 



ore, Red Silver ore. 

 White Iron Pyrites, Brittle Silver ore. 

 Spathic Iron, Calc spar. Dolomite. 



Malachite, Calc spar. White Lead ore. 



ChrysocoUa, White Lead ore. 



To this catalogue we may add the following : — 

 Green earth under the form of Haydenite. 

 Chlorophyllite and Fahlunite under the form of lolite. 

 Eensselaerite under the form of Augite.* 



Psendomorphous changes in the simple salts, produced by a 

 replacement of the acid or base, admit of easy explanation upon 

 the most common principles of chemistry. Such is the change 

 of carbonate of lime to sulphate of lime (gypsum) by the ex- 

 pulsion of the weaker acid (carbonic) by sulphuric acid, and we 

 need only look to some decomposing pyrites (sulphuret of iron) 

 for a source of this acid. Other changes are more difficult of 

 explanation. We propose to run over the most important facts 

 in Dr. Blum's work, as a basis for some farther remarks upon the 

 causes of pseudomorphism, its extent and geological bearing. 

 We take the book in course, and extract such facts as appear of 

 special interest, even if before published, as this subject is not 

 systematically treated in any work in our language. Haidinger's 

 very valuable article on this subject, in volumes IX and X of 

 Brewster's Edinburgh Journal, is the only one of much impor- 

 tance to which we can point. 



Gypsum with the form of Anhydrite. — Large deposits of an- 

 hydrite have undergone this change to gypsum. In the Canaria 



* Another class of Pseudomorphs not particularly distinguished, includes those 

 Vfhich proceed from the change of one form of a dimorphous substance to an- 

 other. Arragonite thus changes to Calc spar without losing its prismatic form. 



