66 Dr. Blum on Pseudomorphous Minerals. 



Art. YII. — On Pseudomorphous Minerals, [Die Pseiidomorpho- 

 sen des Miiieralreichs ;] by Dr. J. Reinhahd Blum. 8vo, pp. 

 378. Stuttgard, 1843. 



Mineral Pseudomorphism is usually considered a curious 

 branch of science, possessing little of that general interest which 

 really attaches to it. The instances of alteration occurring in 

 rocks are often looked upon as confined to isolated crystals, aris- 

 ing from some accidental cause of limited influence. But the 

 developments of the few past years lead us to believe that Pseu- 

 domorphism will soon constitute one of the most important chap- 

 ters in geological treatises. 



The elaborate work by Dr. Blum has prepared the way for 

 more enlarged views on this subject, and opens some insight into 

 this obscure branch of the chemistry of nature. His facts are 

 detailed with great fullness, and show thorough research. All 

 geognostic information bearing upon the origin of these pseudo- 

 morphs is added by him as far as ascertained; and in addition, 

 the nature of the chemical changes undergone is discussed, and 

 various causes suggested for the production of these singular 

 mineral metamorphoses. 



Dr. Blum divides all Pseudomorphs into two classes : — 



I. Pseudomorphs produced by a partial change in the compo- 

 sition of the original mineral. 



II. Pseudomorphs produced by a complete displacement of the 

 original mineral by another. 



In the^rs^ class, one or more elements are removed, added, or 

 introduced by substitution; — and these three modes constitute 

 three divisio?is of this class of Pseudomorphs. As an example 

 of the ^rs^ of these subdivisions we instance Gay-Lussite chang- 

 ed to calc spar by the removal of carbonate of soda and water ; 

 the second, anhydrite, changed to gypsum by the addition of 

 water ; the third, gypsum changed to calc spar, by the substitU' 

 Hon of sulphuric acid for carbonic acid. 



In the second class, to form the pseudomorph, the original min- 

 eral is wholly removed and replaced by another. 



The following catalogue contains the various examples enu- 

 merated by Dr. Blum of these different kinds of Pseudomorphs. 



