STUDIES IN HYDROTHERMAL ALTERATION 183 



best course to adopt is to use minerals of as high degree of purity 

 as are available. The fusion of such a mineral before its investi- 

 gation must be vigorously condemned because it is well established 

 that the minerals which crystallize from a melt are not always like 

 those which were originally fused, and in many cases several dis- 

 tinct minerals are produced by this process from a single species. 

 If the glass that is formed by the fusion is used, it may differ 

 chemically from the original mineral by the loss of volatile gases, 

 and it must differ in its energy content. 



For example, Lemberg's 1 important work is in part open to these 

 criticisms, though the volume of data supplied by him is remarkable. 

 Other work of this sort has been carried on in glass containers which 

 of themselves may have furnished a most important source of error. 

 Further, the concentrations of the solutions which have been used, 

 as a rule, have been far in excess of those known to exist in ground 

 or hot spring waters. Just how much difference this would make 

 in the results obtained is not yet clear, though it is highly probable 

 that the solutions as they come direct from the magma are far more 

 concentrated than those which appear at the surface in the form of 

 hot springs. It is also recognized that such solutions, after having 

 been in contact with the wall rock throughout their courses, have 

 probably changed notably their compositions and concentrations 

 and may bear but small traces of some of their original constituents. 

 As a result of these considerations it is at present an open question 

 how much geologic significance is to be attached to investigations 

 carried on with such concentrations as Lemberg used, though his 

 results have thrown much light on methods of attacking the prob- 

 lem of mineral alteration. Other investigators, especially Thugutt, 2 

 Konigsberger and Miiller, 3 Friedel and Grandjean, 4 Baur, 5 and 

 Chroustschoff, 6 have contributed highly suggestive data. 



1 J. Lemberg, Zeit. deut. geo.. Ges., Vols. XXXV, XXXVII, XXXIX, LX. 



2 J. S. Thugutt, Zeit. anorg. Chem., II, 64-107, 1 13-16; Neues Jahrb. Min. Geol., 

 Beil. Bd. IX, 554-624. 



3 Konigsberger and Miiller, Centralbl. Min., 1906, pp. 339-48, 353-72. 



4 Friedel and Grandjean, Bull. Soc. Min., XXXII, 150-54. 



s Emil Baur, Zeit. physik. Chem., LXI, 567-76; Zeit. anorg. Client., LXXII, 119-61. 

 6 K. von Chroustschoff, Compt. Rend., CXII, 677-79. 



